A complete, college-level introduction to public health, the science and practice of protecting and improving the health of whole populations. The course begins with what public health is and how it differs from clinical medicine, then traces the field's history from sanitation reform and John Snow's cholera investigation through the germ theory to the chronic diseases of today, and it…

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Module 1: Foundations of Public Health

What public health is and how it differs from medicine, where the field came from and how it is organized through core functions and essential services, and the determinants of health and the pursuit of health equity.

What Is Public Health?

Define public health and explain its focus on populations rather than individual patients.
Distinguish public health from clinical medicine in its goals, methods, and unit of concern.
Describe the prevention framework of primary, secondary, and tertiary prevention.

The big picture

Public health is the science and practice of protecting and improving the health of whole populations rather than treating one patient at a time. Where a physician asks what is wrong with this person and how to cure it, a public health professional asks why some groups fall ill more than others and how to prevent that illness before it starts. The field spans clean water and safe food, vaccination and disease surveillance, tobacco policy and road safety, and the social conditions that shape how long and how well people live. This lesson defines the field and sets it beside clinical medicine.

Key idea: Public health works at the level of populations and emphasizes prevention, asking not only how to treat disease but how to keep it from occurring.

A population, not a patient

The defining unit of public health is the population, a defined group such as the residents of a city, the workers in an industry, or the children of a nation. C.-E. A. Winslow's classic 1920 definition still holds: public health is the science and art of preventing disease, prolonging life, and promoting health through the organized efforts of society. Two phrases carry the weight. Organized efforts means health is pursued collectively, through institutions and policies, not by individuals alone. Society means the responsibility is shared. A clean water system protects everyone who drinks from the tap, whether or not any single person asked for it.

Key idea: Public health improves health through organized, collective action aimed at populations rather than through the care of individuals alone.

Public health and medicine compared

Public health and medicine are partners that work differently. Medicine is largely curative and individual, as a clinician diagnoses and treats the patient in front of them. Public health is largely preventive and collective, as it studies patterns across groups and intervenes in the conditions that produce those patterns. The physician George Engel argued that even clinical medicine needs a wider lens than a purely biological one, a biopsychosocial model that includes a patient's circumstances. Public health takes that wider lens as its starting point, asking about housing, income, environment, and policy, not only biology. The two fields need each other, and the strongest health systems combine them.

Key idea: Medicine tends to cure individuals while public health tends to prevent disease across populations, and effective health systems rely on both.

The prevention framework

Public health organizes its work around three levels of prevention. Primary prevention stops a disease or injury before it occurs, as vaccination prevents infection and seatbelt laws prevent crash injuries. Secondary prevention detects and treats a problem early, before symptoms or serious harm, as cancer screening or blood pressure checks do. Tertiary prevention limits damage once disease is established, as cardiac rehabilitation reduces further heart attacks. Each level matters, but public health places special weight on primary prevention, because stopping harm at the source is usually cheaper, fairer, and more effective than treating its consequences later.

Key idea: Prevention runs from primary before onset, through secondary early detection, to tertiary limiting of harm, with public health emphasizing primary prevention.

Population thinking and the prevention paradox

The epidemiologist Geoffrey Rose drew a lasting distinction between helping sick individuals and shifting the health of whole populations. A high-risk strategy targets the people in greatest danger, such as those with very high blood pressure. A population strategy tries to lower risk a little for everyone, such as reducing salt across the food supply. Rose showed that a large number of people at small risk often produce more cases of disease than a small number at high risk, so modest shifts across a population can prevent more illness than intense effort on a few. This population thinking is central to public health.

Key idea: Rose's insight is that small risk reductions spread across an entire population can prevent more disease than intensive treatment of the highest-risk few.

Why public health is often invisible

Public health suffers from a paradox of success. When it works, nothing happens: the outbreak that never spreads, the child who is never poisoned by lead, the heart attack that never comes. Because prevented events are invisible, the field rarely gets the credit or the funding that dramatic cures attract. Much of the twentieth century's gain in life expectancy came from public health measures such as sanitation, safe food, vaccination, and tobacco control rather than from clinical medicine. Recognizing this hidden work is the first step to understanding why societies invest in health departments, inspectors, and surveillance systems most people never see.

Key idea: Because prevention makes bad outcomes not happen, public health is easy to overlook even though it drives much of the improvement in population health.

Common misconceptions

Public health just means government hospitals or care for the poor. It is the population-level effort to prevent disease and promote health, not a type of clinical care.
Public health and medicine are the same thing. They share goals but differ in unit of concern, methods, and emphasis on prevention.
Prevention only means telling people to make healthy choices. Much prevention is structural, such as clean water, safe roads, and food safety, that protects people regardless of individual choices.
If life expectancy rose, doctors must get the credit. Most historical gains came from sanitation, nutrition, and vaccination, which are public health achievements.

Recap

Public health protects and improves the health of populations, emphasizing prevention.
Winslow defined it as preventing disease and promoting health through the organized efforts of society.
Medicine tends to cure individuals, while public health tends to prevent disease across groups.
Prevention runs from primary through secondary to tertiary, with primary prevention emphasized.
Rose's population strategy shows small changes across many people can prevent more disease than targeting a few.

Sources

Winslow, C.-E. A. (1920). The untilled fields of public health. Science, 51(1306), 23-33. doi.org/10.1126/science.51.1306.23
Engel, G. L. (1977). The need for a new medical model: A challenge for biomedicine. Science, 196(4286), 129-136. doi.org/10.1126/science.847460
American Public Health Association. (n.d.). What is public health? apha.org
CDC Foundation. (n.d.). What is public health? cdcfoundation.org
World Health Organization. (n.d.). Constitution of the World Health Organization. who.int

Key terms
Public health: The science and practice of preventing disease, prolonging life, and promoting health through the organized efforts of society.
Population: A defined group of people, such as a city's residents or a nation's children, that is the unit of concern in public health.
Primary prevention: Action that stops disease or injury before it occurs, such as vaccination or seatbelt laws.
Secondary prevention: Early detection and treatment of a health problem before serious harm, such as screening for cancer or high blood pressure.
Tertiary prevention: Efforts to limit disability and complications once disease is established, such as cardiac rehabilitation.
Population strategy: Rose's approach of lowering risk slightly across a whole population rather than targeting only high-risk individuals.
Prevention paradox: The observation that a measure bringing large benefit to a population may offer little apparent benefit to each participating individual.

The History, Core Functions, and Essential Services of Public Health

Summarize key milestones in the history of public health, from sanitation reform to the germ theory and beyond.
Describe the three core functions of public health: assessment, policy development, and assurance.
Explain the ten essential public health services and the idea of public health infrastructure.

The big picture

Public health did not appear all at once. It grew over centuries from a series of crises and discoveries, from plague and cholera to the germ theory and the chronic diseases of modern life. Its history explains why the field is organized as it is today, around monitoring health, developing policy, and assuring services. This lesson traces that history briefly and then introduces the framework that modern practice uses to organize itself: three core functions and ten essential services. Together they describe what a public health system is supposed to do for the community it serves.

Key idea: Modern public health practice is built on centuries of history and is organized today around three core functions and ten essential services.

From miasma to microbes

For most of history, disease was blamed on miasma, or bad air. That mistaken idea still produced useful action, because cleaning up filth did reduce disease. In the nineteenth century, reformers such as Edwin Chadwick pushed for sanitation, sewers, and clean water in crowded industrial cities. In 1854 the physician John Snow traced a London cholera outbreak to a single contaminated water pump on Broad Street, an early triumph of epidemiology that pointed to water, not air, as the cause. Later, the germ theory of Louis Pasteur and Robert Koch identified the microorganisms behind infection, giving sanitation a scientific foundation and launching modern public health.

Key idea: Early public health advanced through sanitation reform and John Snow's cholera investigation, then gained a scientific basis from the germ theory of disease.

The twentieth century and beyond

The twentieth century widened the field. Vaccination, safe food and water, and antibiotics drove down deaths from infectious disease, and life expectancy rose dramatically. As people lived longer, chronic diseases such as heart disease and cancer became the leading killers, and public health expanded into tobacco control, nutrition, and injury prevention. In 1988 a landmark report from the Institute of Medicine, The Future of Public Health, warned that the United States public health system was in disarray and defined its core functions. More recently, the Public Health 3.0 initiative called on health departments to act as community chief health strategists, working across sectors on the social conditions that shape health.

Key idea: As infectious deaths fell and chronic disease rose, public health broadened, and reports like The Future of Public Health and Public Health 3.0 redefined its mission.

Three core functions

The 1988 Institute of Medicine report distilled public health into three core functions. Assessment means monitoring the health of the community, collecting and analyzing data to understand problems and their causes. Policy development means using that evidence to build sound policies and set priorities, in partnership with the community. Assurance means making sure that needed health services are actually available and effective, whether provided by government or others. These three functions, assessment, policy development, and assurance, remain the backbone of how public health agencies define their responsibilities.

Key idea: Public health rests on three core functions: assessing community health, developing evidence-based policy, and assuring that necessary services are available.

The ten essential public health services

To make the core functions concrete, public health uses a framework of ten essential public health services, first issued in 1994 and updated in 2020. They include assessing and monitoring population health, investigating health hazards, communicating to inform and educate, mobilizing partnerships, creating policies and plans, enforcing laws that protect health, connecting people to needed services, building a capable workforce, evaluating and improving programs, and maintaining the organizational and financial infrastructure that supports the rest. The 2020 update placed equity at the center, insisting that these services be provided so everyone can achieve good health. The list is a practical checklist for what a functioning public health system does.

Key idea: The ten essential public health services translate the core functions into concrete tasks, with the 2020 revision putting health equity at the center.

Infrastructure and the health impact pyramid

Delivering these services requires infrastructure, meaning the workforce, data systems, laboratories, and funding that make action possible. It also requires choosing interventions wisely. Thomas Frieden's health impact pyramid ranks actions by their reach and the effort they demand of individuals. At the base sit socioeconomic factors and changes that make healthy choices the default, such as clean water and smoke-free air, which affect whole populations. Near the top sit counseling and clinical care, which help one person at a time. Frieden argued that interventions at the base, though less visible, usually produce the greatest population health gains, echoing the theme that prevention at the source is most powerful.

Key idea: Public health depends on infrastructure, and Frieden's health impact pyramid shows that population-wide changes at the base yield larger gains than one-on-one care at the top.

Common misconceptions

Public health began with modern medicine. Its roots lie in sanitation and reform well before the germ theory, and much of its early success predated antibiotics.
John Snow proved the germ theory. Snow linked cholera to contaminated water before germs were understood, using careful mapping and epidemiology.
The core functions are just paperwork. Assessment, policy development, and assurance describe the essential work every health department must do.
More clinical care is always the best way to improve health. Frieden's pyramid shows population-level changes usually help more people for less effort.

Recap

Public health grew from sanitation reform, Snow's cholera investigation, and the germ theory.
As infectious deaths fell, chronic disease rose and the field broadened.
The 1988 Future of Public Health report named three core functions: assessment, policy development, and assurance.
The ten essential public health services make those functions concrete, with equity now at the center.
Frieden's health impact pyramid ranks population-wide changes above individual clinical care for reach.

Sources

Frieden, T. R. (2010). A framework for public health action: The health impact pyramid. American Journal of Public Health, 100(4), 590-595. doi.org/10.2105/AJPH.2009.185652
DeSalvo, K. B., Wang, Y. C., Harris, A., Auerbach, J., Koo, D., & O'Carroll, P. (2017). Public Health 3.0: A call to action for public health to meet the challenges of the 21st century. Preventing Chronic Disease, 14, 170017. doi.org/10.5888/pcd14.170017
Centers for Disease Control and Prevention. (n.d.). 10 essential public health services. cdc.gov
Centers for Disease Control and Prevention. (n.d.). CDC Museum: Public health timeline. cdc.gov
National Academies of Sciences, Engineering, and Medicine. (n.d.). Health and medicine. nationalacademies.org

Key terms
Miasma theory: The mistaken belief that disease came from bad air, which nonetheless motivated useful sanitation reforms.
Germ theory: The scientific understanding, established by Pasteur and Koch, that specific microorganisms cause infectious disease.
Assessment: The core function of monitoring community health by collecting and analyzing data on problems and their causes.
Policy development: The core function of using evidence to build health policy and set priorities with the community.
Assurance: The core function of ensuring that needed health services are available and effective.
Ten essential public health services: A framework of ten activities, updated in 2020 with equity at its center, that a public health system should perform.
Health impact pyramid: Frieden's model ranking interventions by reach, from population-wide changes at the base to individual care at the top.

Determinants of Health and Health Equity

Identify the major determinants of health and explain why medical care is only one of them.
Describe the social determinants of health and the idea of the causes of the causes.
Distinguish health disparities from health inequities and define health equity.

The big picture

Why are some groups so much healthier than others? Two neighborhoods a few miles apart can differ in life expectancy by a decade or more. The answer is not mainly the hospitals nearby. Health is shaped by a broad set of determinants, including genes and behavior but also income, education, housing, environment, and the policies that distribute them. When those conditions are unfair and avoidable, the resulting differences in health are called inequities. This lesson explains what determines health, introduces the social determinants, and defines the equity concepts that guide much of modern public health.

Key idea: Health is shaped by many determinants beyond medical care, and unfair, avoidable differences in health are called inequities.

What determines health

Researchers group the determinants of health into several categories: genetics and biology, individual behavior, the physical environment, social and economic conditions, and access to medical care. Studies consistently find that medical care accounts for a relatively small share of health outcomes, often estimated at only ten to twenty percent, while behavior and social and economic conditions account for much more. This does not make care unimportant. It means that a society trying to improve health cannot rely on clinics alone. Where people live, learn, work, and play shapes their health long before they ever reach a doctor.

Key idea: Medical care explains only a small part of health outcomes, while behavior, environment, and social and economic conditions explain much more.

The social determinants of health

The social determinants of health are the conditions in which people are born, grow, live, work, and age. Healthy People 2030 groups them into five domains: economic stability, education access and quality, health care access and quality, neighborhood and built environment, and social and community context. Braveman and Gottlieb call these the causes of the causes. High blood pressure may be the cause of a stroke, but low income, chronic stress, and a neighborhood without safe places to exercise or affordable healthy food are the causes of that high blood pressure. Public health tries to reach those deeper causes.

Key idea: Social determinants are the everyday conditions that shape health, and they act as the causes of the causes behind individual risk factors.

The social gradient

Health does not simply divide into the sick poor and the healthy rich. Michael Marmot's studies of British civil servants, the Whitehall studies, found a social gradient. At every step up the occupational ladder, health improved, even among people who were all employed and none of them poor. Those one rung from the top were healthier than those two rungs down, and so on. The gradient shows that relative position, control over one's work, and social circumstances affect health across the whole of society, not only at the bottom. It reframes health inequity as a broad social issue rather than a problem of the poorest alone.

Key idea: Marmot's social gradient shows that health improves step by step with social position across an entire population, not only between rich and poor.

Disparities, inequities, and equity

Careful language matters here. A health disparity is any difference in health between groups. A health inequity is a difference that is unfair and avoidable, rooted in social disadvantage rather than biology or free choice. Braveman and Gruskin define equity as the absence of systematic disparities between groups with different levels of social advantage. Health equity is the goal of giving everyone a fair opportunity to be healthy, which often requires unequal effort, directing more resources to those who start with less. Equity is therefore not the same as equality. Treating everyone identically can leave existing unfair gaps in place.

Key idea: A disparity is any group difference in health, an inequity is an unfair and avoidable one, and equity means a fair opportunity for health that may require unequal resources.

Acting on the determinants

Because the determinants lie largely outside the clinic, public health looks upstream. A downstream response treats people after they are harmed. An upstream response changes the conditions that cause harm, such as raising incomes, improving schools, cleaning the air, or making healthy food affordable. Tools like the County Health Rankings show communities how factors such as education, employment, and the physical environment predict health outcomes, helping local leaders act. Working upstream is slower and more political than treating patients, but it reaches the roots of poor health and can reduce inequities that clinical care alone cannot touch.

Key idea: Public health acts upstream, changing the social and economic conditions that produce disease rather than only treating people after they are harmed.

Common misconceptions

Health is mostly determined by the medical care you receive. Care matters, but behavior and social and economic conditions explain far more of health outcomes.
Health inequities are just the result of personal choices. Choices are shaped by conditions, and inequities are the unfair, avoidable differences rooted in social disadvantage.
Only the poorest people have worse health. The social gradient shows health improves at every step up the social ladder.
Equity and equality mean the same thing. Equity may require giving more to those who start with less, not treating everyone identically.

Recap

Health is shaped by genes, behavior, environment, social and economic conditions, and care, with care a small share.
Social determinants are the conditions of daily life and act as the causes of the causes.
Marmot's social gradient shows health rising with social position across society.
Disparities are group differences, inequities are unfair and avoidable ones, and equity is a fair opportunity for health.
Public health acts upstream on the determinants rather than only treating harm downstream.

Sources

Braveman, P., & Gottlieb, L. (2014). The social determinants of health: It's time to consider the causes of the causes. Public Health Reports, 129(Suppl 2), 19-31. doi.org/10.1177/00333549141291S206
Marmot, M. (2005). Social determinants of health inequalities. The Lancet, 365(9464), 1099-1104. doi.org/10.1016/S0140-6736(05)71146-6
Braveman, P., & Gruskin, S. (2003). Defining equity in health. Journal of Epidemiology & Community Health, 57(4), 254-258. doi.org/10.1136/jech.57.4.254
Office of Disease Prevention and Health Promotion. (n.d.). Social determinants of health. Healthy People 2030. odphp.health.gov
World Health Organization. (n.d.). Social determinants of health. who.int
County Health Rankings & Roadmaps. (n.d.). Model of health. University of Wisconsin Population Health Institute. countyhealthrankings.org

Key terms
Determinants of health: The range of factors that shape health, including genetics, behavior, environment, social and economic conditions, and medical care.
Social determinants of health: The conditions in which people are born, grow, live, work, and age that shape their health.
Causes of the causes: Braveman and Gottlieb's phrase for the social conditions underlying individual risk factors and disease.
Social gradient: The stepwise improvement in health at each higher level of social and economic position, shown by Marmot's Whitehall studies.
Health disparity: Any measurable difference in health status between population groups.
Health inequity: A health difference that is unfair and avoidable because it is rooted in social disadvantage.
Health equity: The principle that everyone should have a fair opportunity to be healthy, which may require unequal resources.

Module 2: Epidemiology and Data in Public Health

The tools public health uses to see: epidemiology and its measures of disease frequency, the study designs and causal reasoning that move from association to cause, and the biostatistics, surveillance, and data systems that turn observation into evidence.

Epidemiology: Measuring Health and Disease

Define epidemiology and explain its role as the basic science of public health.
Distinguish incidence from prevalence and explain when each measure is used.
Interpret common measures of disease frequency, including ratios, proportions, and rates.

The big picture

If public health is about populations, someone has to measure those populations, counting who is sick, who dies, and how these numbers differ across places and groups. That counting is the work of epidemiology, often called the basic science of public health. Epidemiology turns scattered cases into patterns, and patterns into clues about causes and solutions. Before a health department can act on an outbreak, a rise in overdoses, or a gap in life expectancy, it must measure the problem clearly. This lesson introduces epidemiology and the core measures of disease frequency that every public health analysis depends on.

Key idea: Epidemiology is the basic science of public health, measuring how health and disease are distributed across populations.

What epidemiology is

Epidemiology is the study of the distribution and determinants of health-related states in populations, applied to control health problems. Distribution refers to patterns by person, place, and time: who is affected, where, and when. Determinants are the causes and risk factors that explain those patterns. Descriptive epidemiology maps the patterns, describing an outbreak by age, location, and date. Analytic epidemiology tests explanations, comparing groups to find causes. A useful habit is to ask of any health claim: what population, measured how, compared with what. Those questions separate careful evidence from anecdote.

Key idea: Epidemiology studies the distribution and determinants of health in populations, using person, place, and time to describe patterns and comparison to explain them.

Counts, ratios, proportions, and rates

A raw count, such as 300 flu cases, means little without context. To interpret it, epidemiologists relate the count to the population at risk. A ratio divides one quantity by another that need not include it, such as male cases divided by female cases. A proportion is a ratio in which the numerator is part of the denominator, such as the share of cases who were hospitalized. A rate measures how fast events occur in a population over time, such as cases per 100,000 people per year. The denominator is what makes a number comparable across places of different sizes.

Key idea: Meaningful measures relate a count to the population at risk through ratios, proportions, and rates, so the denominator is as important as the numerator.

Incidence and prevalence

Two measures anchor the study of disease frequency. Incidence counts new cases that develop over a period, capturing the risk of getting a disease. Prevalence counts all existing cases at a point in time, capturing how widespread a disease is. The two are linked, because prevalence roughly equals incidence multiplied by average duration. A disease that is quickly cured or quickly fatal has low prevalence even if incidence is high, while a chronic disease can have high prevalence from a modest incidence because cases accumulate. Confusing the two is a common error. Incidence is the measure for studying causes, prevalence for planning services.

Key idea: Incidence measures new cases and risk, prevalence measures existing cases and burden, and prevalence rises with both incidence and duration.

Measuring death and burden

Public health also measures death and lost health. A mortality rate is deaths per unit of population over time. The case fatality rate is the share of people with a disease who die from it, a measure of severity. Because deaths at young ages arguably represent a greater loss, analysts also compute years of potential life lost, which weights early deaths more heavily. Beyond death, morbidity measures illness and disability, and combined measures such as the disability-adjusted life year capture both dying early and living with poor health. These measures let public health compare very different conditions on a common scale.

Key idea: Mortality rates, case fatality, years of potential life lost, and disability measures together capture both death and the burden of living with illness.

Comparing populations fairly

Comparisons can mislead if populations differ in structure, especially in age. An area full of retirees will have a higher crude death rate than a college town, even if people of the same age are equally healthy in both. To compare fairly, epidemiologists use age-adjusted, or standardized, rates that remove the effect of differing age distributions. A crude rate describes the actual burden in a place, useful for planning services. An age-adjusted rate is better for comparing risk between populations or over time. Knowing which rate is being reported prevents false conclusions about who is healthier.

Key idea: Age-adjusted rates allow fair comparison between populations with different age structures, while crude rates describe the actual burden in a place.

Common misconceptions

Incidence and prevalence are the same. Incidence counts new cases over time, while prevalence counts all existing cases at a moment.
A high case count proves a place is unhealthy. Without a denominator, a count says nothing about risk, since larger places have more cases.
A rising prevalence always means rising risk. Prevalence can rise simply because people with a disease live longer, not because more people get it.
A higher crude death rate means people there are less healthy. Differences in age structure can drive crude rates, which is why age-adjusted rates are used for comparison.

Recap

Epidemiology is the basic science of public health, studying distribution and determinants.
Descriptive epidemiology uses person, place, and time; analytic epidemiology compares groups to find causes.
Ratios, proportions, and rates relate counts to the population at risk.
Incidence measures new cases and risk, while prevalence measures existing cases and burden.
Age-adjusted rates allow fair comparison across populations with different age structures.

Sources

Rose, G. (1985). Sick individuals and sick populations. International Journal of Epidemiology, 14(1), 32-38. doi.org/10.1093/ije/14.1.32
Centers for Disease Control and Prevention. (2012). Measures of risk (frequency measures). In Principles of epidemiology in public health practice (3rd ed., Lesson 3). archive.cdc.gov
Centers for Disease Control and Prevention. (2012). Morbidity frequency measures. In Principles of epidemiology in public health practice (3rd ed., Lesson 3). archive.cdc.gov
Centers for Disease Control and Prevention. (2012). Mortality frequency measures. In Principles of epidemiology in public health practice (3rd ed., Lesson 3). archive.cdc.gov
Centers for Disease Control and Prevention. (2012). Principles of epidemiology in public health practice (3rd ed.). archive.cdc.gov

Key terms
Epidemiology: The study of the distribution and determinants of health-related states in populations, applied to control health problems.
Descriptive epidemiology: The description of health patterns by person, place, and time.
Analytic epidemiology: The comparison of groups to identify causes and risk factors of disease.
Incidence: The number of new cases of a disease that develop in a population over a period of time.
Prevalence: The number of existing cases of a disease in a population at a given point in time.
Rate: A measure of how frequently events occur in a population over time, such as cases per 100,000 per year.
Age-adjusted rate: A summary rate statistically standardized to remove the effect of differing age distributions, allowing fair comparison.

Study Designs and Causal Inference

Compare the major epidemiologic study designs and their strengths and limits.
Explain how association differs from causation and what confounding and bias are.
Apply the Bradford Hill considerations to reason about whether an association is causal.

The big picture

Once a health problem is measured, the next question is why. Answering it means designing studies that compare groups, and then reasoning carefully about whether an observed link is truly a cause. This is among the hardest work in public health, because the world rarely runs clean experiments on people. A pattern can arise from a real cause, from a hidden third factor, from bias in how data were collected, or from pure chance. This lesson surveys the main study designs epidemiologists use and the logic they apply to move from association to a claim about causation.

Key idea: Public health uses different study designs to compare groups and a careful logic to judge whether an association reflects a true cause.

Descriptive and observational designs

Studies range from simple description to controlled experiment. A case report describes a single striking patient and can raise an alarm, but proves little. A cross-sectional study measures exposure and disease at one moment, good for prevalence but weak on cause because it cannot tell which came first. A case-control study starts with people who have a disease and compares their past exposures with those of similar people without it, efficient for rare diseases. A cohort study follows exposed and unexposed groups forward to see who develops disease, strong for timing but slow and costly. Each design trades speed and cost against strength of evidence.

Key idea: Observational designs from case reports to case-control and cohort studies differ in how well they establish the timing and strength of a suspected cause.

Experiments and the randomized trial

The strongest design for cause is the experiment, in which the investigator assigns the exposure. In a randomized controlled trial, participants are randomly assigned to receive an intervention or not. Randomization tends to balance both known and unknown differences between groups, so a later difference in outcome can be credited to the intervention. Trials underpin decisions about drugs, vaccines, and some programs. But experiments are not always possible or ethical, since no one can be assigned to smoke or to live in poverty. As Nick Black argued, well-designed observational studies remain essential where trials cannot be run.

Key idea: Randomized trials give the strongest evidence for cause by balancing groups, but observational studies are essential where experiments are impossible or unethical.

Association is not causation

Finding that two things occur together does not prove one causes the other. Several rival explanations must be ruled out. Chance can produce a spurious link, which statistics help assess. Bias, a systematic error in selecting participants or measuring variables, can create a false association. Confounding occurs when a third factor is linked to both the exposure and the outcome, as coffee drinkers who also smoke may seem to have more disease from coffee when smoking is the real cause. Reverse causation mistakes effect for cause. Good studies anticipate these threats through design and analysis, but no single study is ever the last word.

Key idea: An association can arise from chance, bias, confounding, or reverse causation, so a correlation is not by itself evidence of a cause.

The Bradford Hill considerations

In 1965 Austin Bradford Hill offered a set of considerations for judging whether an association is likely causal. They include the strength of the association, its consistency across studies and settings, its specificity, the correct temporal order with cause preceding effect, a biological gradient in which more exposure brings more disease, plausibility, coherence with existing knowledge, experimental evidence, and analogy. Hill stressed that these are viewpoints, not a checklist to be scored, and that temporal order is the one true requirement. Used thoughtfully, they structure the debate over whether to treat an exposure as a cause worth acting on.

Key idea: Bradford Hill's considerations, including strength, consistency, temporality, and a dose-response gradient, guide judgment about causation without serving as a rigid checklist.

A worked example: smoking and lung cancer

The link between smoking and lung cancer shows the logic in action. No one could randomly assign people to smoke for decades. Instead, Richard Doll and Austin Bradford Hill followed a large cohort of British doctors and found that death rates from lung cancer rose steadily with the amount smoked, a clear biological gradient. The association was strong, consistent across many studies, temporally correct, and biologically plausible. Together this evidence built a causal case powerful enough to justify decades of tobacco control, even without a randomized trial. It remains a model of how public health reasons from observation to action.

Key idea: The cohort evidence linking smoking to lung cancer shows how strength, consistency, temporality, and dose-response can establish causation without an experiment.

Common misconceptions

Correlation proves causation. An association may reflect chance, bias, confounding, or reverse causation rather than a true cause.
Only randomized trials can show causes. Trials are strongest, but observational studies established many causes, including smoking and lung cancer, where trials were impossible.
Bradford Hill's points are a scoring checklist. Hill described them as viewpoints for judgment, with temporal order the only strict requirement.
A confounder is just a measurement mistake. Confounding is a real third factor linked to both exposure and outcome, not simply an error.

Recap

Study designs range from case reports through cross-sectional, case-control, and cohort studies to experiments.
Randomized trials balance groups and give the strongest evidence for cause.
Association is not causation, because chance, bias, confounding, and reverse causation can mislead.
Bradford Hill's considerations guide judgment about causation, with temporality required.
Smoking and lung cancer show how observational evidence can establish a cause.

Sources

Hill, A. B. (1965). The environment and disease: Association or causation? Proceedings of the Royal Society of Medicine, 58(5), 295-300. doi.org/10.1177/003591576505800503
Doll, R., & Hill, A. B. (1954). The mortality of doctors in relation to their smoking habits. BMJ, 1(4877), 1451-1455. doi.org/10.1136/bmj.1.4877.1451
Black, N. (1996). Why we need observational studies to evaluate the effectiveness of health care. BMJ, 312(7040), 1215-1218. doi.org/10.1136/bmj.312.7040.1215
Centers for Disease Control and Prevention. (2012). Analytic epidemiology (study designs). In Principles of epidemiology in public health practice (3rd ed., Lesson 1). archive.cdc.gov
Centers for Disease Control and Prevention. (2012). Causation. In Principles of epidemiology in public health practice (3rd ed., Lesson 1). archive.cdc.gov

Key terms
Cohort study: An observational study that follows exposed and unexposed groups over time to compare who develops disease.
Case-control study: A study that compares the past exposures of people with a disease to those of similar people without it.
Randomized controlled trial: An experiment in which participants are randomly assigned to an intervention or comparison, balancing groups.
Confounding: Distortion of an association by a third factor related to both the exposure and the outcome.
Bias: A systematic error in the selection of participants or the measurement of variables that distorts results.
Bradford Hill considerations: A set of viewpoints, including strength, consistency, temporality, and dose-response, used to judge whether an association is causal.
Temporality: The requirement that a cause precede its effect in time, the one strict condition for causation.

Biostatistics and Data in Public Health

Explain the role of biostatistics in turning public health data into evidence.
Interpret variability, confidence intervals, and the meaning and limits of a p-value.
Describe public health surveillance and the main sources of population health data.

The big picture

Numbers do not speak for themselves. A difference between two groups might reflect a real effect or just the play of chance in a limited sample. Biostatistics is the branch of statistics applied to health and biology, and it gives public health the tools to describe data honestly and to judge how much confidence a finding deserves. It also underlies surveillance, the ongoing collection of health data that lets a society notice a rising overdose rate or a new outbreak. This lesson introduces statistical thinking at a conceptual level and the data systems that feed it, without heavy mathematics.

Key idea: Biostatistics turns raw public health data into trustworthy evidence and supports the surveillance systems that monitor a population's health.

Describing data: center and spread

The first task is to summarize. A measure of center, such as the mean or the median, describes a typical value. The median, the middle value, is often preferred when data are skewed, as income and hospital costs usually are, because a few extreme values pull the mean upward. Just as important is spread, the variability around the center, described by the range or standard deviation. Two towns can share an average income yet differ sharply in inequality. Public health cares about spread because averages can hide the very disparities the field exists to address. A distribution shows the full shape of the data.

Key idea: Data are summarized by a measure of center and a measure of spread, and the median and variability often reveal what an average alone conceals.

From sample to population: uncertainty

Public health usually studies a sample and wants to say something about a whole population. Because a sample is only part of the picture, every estimate carries uncertainty. A confidence interval expresses that uncertainty as a range of plausible values for the true figure, for instance a vaccination rate estimated at 72 percent with a 95 percent confidence interval from 69 to 75 percent. A wide interval signals a small or noisy sample and warns against strong conclusions. Reporting an interval, rather than a single number, is more honest because it shows how precisely the quantity is actually known.

Key idea: Estimates from samples carry uncertainty, and a confidence interval communicates the range of plausible true values more honestly than a single number.

Significance and its limits

To ask whether a result could be due to chance, researchers often compute a p-value, the probability of seeing a result at least as extreme if there were truly no effect. A small p-value suggests the result is unlikely to be mere chance. But significance testing is widely misused. As Sterne and Davey Smith argued, a p-value is not the probability that a hypothesis is true, and statistical significance is not the same as practical importance. A tiny, meaningless difference can be significant in a huge sample, while an important effect can miss significance in a small one. Sound analysis reports effect sizes and intervals, not p-values alone.

Key idea: A p-value gauges whether chance alone could explain a result, but statistical significance is not the same as practical importance and is easily misused.

Public health surveillance

Surveillance is the ongoing, systematic collection, analysis, and interpretation of health data, tied to action. Thacker and Berkelman described it as information for action, the nervous system of public health. Clinicians and laboratories report notifiable diseases such as measles or tuberculosis to health departments, which watch for unusual patterns and respond. Surveillance also tracks chronic disease, injuries, and behaviors. Its value lies not in collecting data for its own sake but in feeding decisions, closing the loop from observation to intervention. A rise detected early can mean an outbreak contained before it spreads widely.

Key idea: Surveillance is the continuous collection and interpretation of health data for action, functioning as the information system that lets public health detect and respond to threats.

Sources of data and their limits

Public health draws on many data sources. Vital statistics record births and deaths. Surveys measure behaviors and conditions in representative samples of the population. Disease registries track conditions like cancer. Tools such as CDC WONDER make much of this public. Every source has limits, including undercounting, reporting delays, and gaps for small or marginalized groups whose data may be missing or misclassified. Because policy follows data, missing data can mean missing people. A growing priority is disaggregating data by race, ethnicity, and other factors so that inequities become visible rather than hidden inside averages.

Key idea: Vital statistics, surveys, and registries all inform public health, but each has limits, and gaps in data can render disadvantaged groups invisible to policy.

Common misconceptions

The average tells the whole story. Averages hide spread and can mask the disparities public health exists to address. find source ↗
A confidence interval is a guarantee. It is a range of plausible values reflecting sampling uncertainty, not a certainty about the true figure. find source ↗
Statistical significance means a result is important. Significance reflects sample size and chance, not the size or practical value of an effect. find source ↗
More data always means better data. Data can be biased or incomplete, and missing data for some groups can distort policy. find source ↗

Recap

Biostatistics turns public health data into evidence and measures uncertainty.
Data are summarized by center and spread, with the median and variability revealing what averages hide.
Confidence intervals express the uncertainty in estimates drawn from samples.
P-values assess chance but do not measure importance and are easily misused.
Surveillance is information for action, and every data source has limits that can hide disadvantaged groups.

Sources

Sterne, J. A. C., & Davey Smith, G. (2001). Sifting the evidence: What's wrong with significance tests? BMJ, 322(7280), 226-231. doi.org/10.1136/bmj.322.7280.226
Thacker, S. B., & Berkelman, R. L. (1988). Public health surveillance in the United States. Epidemiologic Reviews, 10, 164-190. doi.org/10.1093/oxfordjournals.epirev.a036021
Ioannidis, J. P. A. (2005). Why most published research findings are false. PLoS Medicine, 2(8), e124. doi.org/10.1371/journal.pmed.0020124
Centers for Disease Control and Prevention. (2012). Public health surveillance. In Principles of epidemiology in public health practice (3rd ed., Lesson 5). archive.cdc.gov
Centers for Disease Control and Prevention. (n.d.). CDC WONDER. wonder.cdc.gov

Key terms
Biostatistics: The application of statistics to health and biology, used to describe data and judge the strength of evidence.
Median: The middle value of a dataset, often preferred over the mean when data are skewed by extreme values.
Variability: The spread of data around its center, described by measures such as the range or standard deviation.
Confidence interval: A range of plausible values for a true quantity, expressing the uncertainty of an estimate from a sample.
P-value: The probability of observing a result at least as extreme as the one seen if there were truly no effect.
Public health surveillance: The ongoing, systematic collection, analysis, and interpretation of health data, tied to public health action.
Notifiable disease: A disease that clinicians and laboratories are required to report to health authorities so patterns can be tracked.

Module 3: Preventing Disease and Injury

The major domains where public health prevents harm: infectious disease and the investigation of outbreaks, the chronic diseases that now lead causes of death, the environmental hazards that act on whole populations, and the injuries and violence once dismissed as accidents.

Infectious Disease and Outbreak Investigation

Explain the chain of infection and the modes of disease transmission.
Describe herd immunity and the main strategies to control infectious disease.
Outline the steps of an outbreak investigation.

The big picture

Infectious diseases were the great killers of the past and remain a central concern of public health, as COVID-19 made unmistakably clear. Understanding how infections spread is the key to stopping them. Public health thinks of transmission as a chain that can be broken at several links, and it responds to sudden increases in disease through a structured outbreak investigation. This lesson explains how infectious disease moves through a population, how vaccination and other measures protect communities, and how epidemiologists investigate an outbreak from the first alarm to control.

Key idea: Controlling infectious disease depends on understanding how infection spreads and on the structured methods public health uses to investigate and stop outbreaks.

The chain of infection

Infection spreads through a chain with several links: a pathogen, a reservoir where it lives such as humans, animals, or the environment, a portal of exit, a mode of transmission, a portal of entry, and a susceptible host. Transmission can be direct, as through contact or respiratory droplets, or indirect, as through contaminated food and water, objects, or insect vectors like mosquitoes. Breaking any link stops the spread. Handwashing interrupts transmission, safe water removes a reservoir, and vaccination reduces host susceptibility. Thinking in terms of the chain helps public health choose where to intervene most effectively for a given disease.

Key idea: Infection spreads through a chain of linked steps, and breaking any single link, from reservoir to susceptible host, can stop transmission.

Herd immunity

When enough people in a population are immune, whether through vaccination or prior infection, a pathogen struggles to find new hosts and its spread slows or stops. This indirect protection is called herd immunity, and it shields even those who cannot be vaccinated, such as newborns or people with weakened immune systems. As Fine, Eames, and Heymann explain, the threshold for herd immunity depends on how contagious a disease is. Highly transmissible diseases like measles require very high immunity, above ninety percent, to prevent outbreaks. When vaccination rates fall below the threshold, diseases once controlled can return, as measles outbreaks in under-vaccinated communities show.

Key idea: Herd immunity protects a whole population, including those who cannot be vaccinated, once the immune share rises above a threshold set by how contagious the disease is.

Strategies to control infectious disease

Public health controls infectious disease through several strategies. Vaccination builds immunity before exposure. Sanitation and safe water block environmental transmission. Case finding, isolation of the sick, and quarantine of the exposed limit spread during outbreaks. Contact tracing identifies and warns those who may have been exposed. Antimicrobial treatment cures individuals and can reduce transmission, though overuse drives antibiotic resistance, itself a growing threat. Vector control targets mosquitoes and other carriers. The right mix depends on the pathogen. The reproduction number, the average number of new infections caused by one case, guides how aggressively a community must act to bring an outbreak under control.

Key idea: Infectious disease control combines vaccination, sanitation, isolation and quarantine, contact tracing, treatment, and vector control, chosen according to how the pathogen spreads.

Steps of an outbreak investigation

When cases rise unexpectedly, epidemiologists follow a set sequence. They confirm the outbreak is real and verify the diagnosis, then establish a case definition and count cases. They describe the outbreak by person, place, and time, often using an epidemic curve, a graph of cases over time that hints at the source. From these patterns they form a hypothesis about the cause, test it with analytic studies comparing the ill and the well, and then implement control measures. Communication runs throughout. The Broad Street cholera investigation was an early example, and the same logic guided the response to foodborne outbreaks and COVID-19.

Key idea: An outbreak investigation moves through confirming the outbreak, defining and counting cases, describing patterns, forming and testing a hypothesis, and implementing control.

Emerging and re-emerging threats

New infectious threats keep appearing. Emerging diseases are newly recognized or newly spreading, like HIV, SARS, and COVID-19, while re-emerging diseases are old foes returning, like measles or drug-resistant tuberculosis. Many emerge from animals in a process called zoonotic spillover, and factors such as global travel, crowding, climate change, and antibiotic resistance accelerate their spread. Webster and Govorkova traced how avian influenza viruses evolve and cross into humans, a standing pandemic concern. Surveillance and preparedness, covered later in this course, are the public health answer to a world where the next outbreak is always a flight away.

Key idea: Emerging and re-emerging diseases, many arising from animals, are driven by travel, crowding, and resistance, making surveillance and preparedness essential.

Common misconceptions

Infectious disease is a problem of the past. New and returning pathogens, from COVID-19 to drug-resistant infections, keep it central to public health.
Herd immunity protects only the vaccinated. Its value is indirect protection of those who cannot be vaccinated, once enough others are immune.
Antibiotics can cure any infection. Antibiotics do not work on viruses, and their overuse breeds resistant bacteria.
Outbreak investigation is guesswork. It follows a disciplined sequence of steps from confirming cases to testing a hypothesis and acting.

Recap

Infection spreads through a chain that can be broken at any link.
Transmission may be direct or indirect, including through vectors, food, and water.
Herd immunity protects a population once immunity passes a threshold set by contagiousness.
Control combines vaccination, sanitation, isolation, tracing, treatment, and vector control.
Outbreak investigation follows a structured sequence from confirming the outbreak to implementing control.

Sources

Fine, P., Eames, K., & Heymann, D. L. (2011). Herd immunity: A rough guide. Clinical Infectious Diseases, 52(7), 911-916. doi.org/10.1093/cid/cir007
Webster, R. G., & Govorkova, E. A. (2006). H5N1 influenza: Continuing evolution and spread. New England Journal of Medicine, 355(21), 2174-2177. doi.org/10.1056/NEJMp068205
Centers for Disease Control and Prevention. (2012). Steps of an outbreak investigation. In Principles of epidemiology in public health practice (3rd ed., Lesson 6). archive.cdc.gov
World Health Organization. (n.d.). Infectious diseases. who.int
World Health Organization. (n.d.). Vaccines and immunization. who.int

Key terms
Chain of infection: The linked sequence, from pathogen and reservoir through transmission to a susceptible host, by which infection spreads.
Mode of transmission: The means by which a pathogen passes to a new host, whether direct contact, droplets, vehicles, or vectors.
Herd immunity: Indirect protection of a population when a high enough share is immune that a pathogen cannot spread easily.
Reproduction number: The average number of new infections caused by one case, indicating how fast a disease can spread.
Quarantine: The separation and restriction of movement of people who may have been exposed to a contagious disease.
Contact tracing: Identifying and notifying people who may have been exposed to an infected person so they can take precautions.
Epidemic curve: A graph of the number of cases over time during an outbreak, used to infer its source and pattern.

Chronic Disease Prevention

Explain why chronic diseases are now the leading causes of death and disability.
Identify the major shared risk factors behind chronic disease.
Describe population strategies for preventing chronic disease.

The big picture

Heart disease, cancer, stroke, diabetes, and chronic lung disease now cause most deaths in the United States and much of the world. Unlike a sudden infection, these chronic diseases develop slowly over years and often share a small set of underlying causes. That is both a challenge and an opportunity. Because a few risk factors drive so much disease, changing them across a population can prevent an enormous amount of illness. This lesson explains the rise of chronic disease, the shared risks behind it, and the public health strategies that aim to prevent it rather than only treat its later complications.

Key idea: Chronic diseases are now the leading causes of death, and because they share a few modifiable risk factors, population-wide prevention can avert vast amounts of illness.

The epidemiologic transition

A century ago, infectious diseases killed most people, often in childhood. As sanitation, nutrition, and medicine improved and people lived longer, the leading causes of death shifted to chronic, noncommunicable diseases. Demographers call this shift the epidemiologic transition. Today chronic diseases account for the large majority of deaths and health spending. They are also unequally distributed, striking earlier and harder among lower-income groups and in many low- and middle-income countries now facing a double burden of infectious and chronic disease at once. The transition reframed the central task of public health from fighting epidemics to preventing slow, lifelong diseases.

Key idea: The epidemiologic transition shifted the leading causes of death from infectious to chronic diseases, which now dominate mortality and fall unequally across groups.

Actual causes of death

Listing heart disease or cancer as a cause of death describes the disease, not its origin. In an influential analysis, McGinnis and Foege looked behind the diagnoses to the actual causes of death, the behaviors and exposures that set disease in motion. Mokdad and colleagues later updated the estimates for the year 2000. A short list dominated: tobacco use, poor diet and physical inactivity, and alcohol, together accounting for a large share of deaths. The lesson is powerful. A handful of modifiable risk factors, not hundreds of separate diseases, drive most premature death, so targeting those factors can prevent many diseases at once.

Key idea: McGinnis and Foege and later Mokdad showed that a few behaviors, led by tobacco and poor diet with inactivity, are the actual causes behind most chronic disease deaths.

Shared risk factors

Chronic diseases share a compact set of risk factors. Behavioral risks include tobacco use, unhealthy diet, physical inactivity, and harmful alcohol use. These contribute to intermediate, or metabolic, risks such as high blood pressure, high blood sugar, obesity, and high cholesterol, which in turn lead to heart disease, stroke, diabetes, and some cancers. Because the same risks feed many diseases, one change ripples widely, as reducing smoking cuts heart disease, several cancers, and lung disease together. These risks are themselves shaped by the social and commercial environment, including how food, tobacco, and alcohol are marketed, priced, and made available.

Key idea: A small set of behavioral and metabolic risk factors underlies most chronic disease, so reducing them prevents several diseases simultaneously.

Population strategies for prevention

Because chronic disease risks are widespread and shaped by environment, the most effective prevention works at the population level rather than urging individuals to try harder. Tobacco control shows the model: taxes, smoke-free laws, advertising limits, and warning labels drove smoking down far more than advice alone. Similar approaches apply elsewhere, such as sodium reduction in the food supply, clearer nutrition labels, safe places for physical activity, and policies on sugary drinks. Clinical prevention still matters, including screening and controlling blood pressure, but Rose's logic holds. Shifting the whole population's risk a little usually prevents more disease than treating only the highest-risk individuals.

Key idea: Population strategies such as tobacco taxes, smoke-free laws, and a healthier food environment prevent more chronic disease than appeals to individual willpower alone.

Deaths of despair and mental health

Not all chronic conditions are physical. Depression, anxiety, and substance use disorders cause enormous disability and are increasingly recognized as public health priorities. Case and Deaton documented rising midlife mortality among some Americans from suicide, drug overdose, and alcohol, which they called deaths of despair, linked to eroding economic prospects. Mental health and physical chronic disease often travel together and share social roots. Modern chronic disease prevention therefore reaches beyond individual behavior to the economic and social conditions that shape both, connecting this lesson to the determinants of health explored earlier.

Key idea: Mental health and substance use disorders are major chronic conditions, and deaths of despair show how economic and social conditions drive chronic disease and premature death.

Common misconceptions

Chronic diseases are just bad luck or old age. Most are strongly shaped by modifiable risk factors and social conditions, not age alone.
Chronic disease is only a rich-country problem. Low- and middle-income countries now bear a large and rising chronic disease burden.
Prevention means telling people to eat better and exercise. The most effective prevention changes the environment through policy, not willpower alone.
Mental health is separate from public health. Mental and physical chronic conditions share social roots and are central public health concerns.

Recap

The epidemiologic transition made chronic diseases the leading causes of death.
A few actual causes, led by tobacco and poor diet with inactivity, drive most premature death.
Chronic diseases share behavioral and metabolic risk factors, so one change prevents several diseases.
Population strategies such as tobacco control outperform appeals to individual willpower.
Mental health and deaths of despair show the social roots of chronic disease.

Sources

Mokdad, A. H., Marks, J. S., Stroup, D. F., & Gerberding, J. L. (2004). Actual causes of death in the United States, 2000. JAMA, 291(10), 1238-1245. doi.org/10.1001/jama.291.10.1238
McGinnis, J. M., & Foege, W. H. (1993). Actual causes of death in the United States. JAMA, 270(18), 2207-2212. doi.org/10.1001/jama.1993.03510180077038
Case, A., & Deaton, A. (2015). Rising morbidity and mortality in midlife among white non-Hispanic Americans in the 21st century. Proceedings of the National Academy of Sciences, 112(49), 15078-15083. doi.org/10.1073/pnas.1518393112
Centers for Disease Control and Prevention. (n.d.). About chronic diseases. cdc.gov
World Health Organization. (n.d.). Noncommunicable diseases. who.int

Key terms
Chronic disease: A long-lasting, generally noncommunicable condition such as heart disease, cancer, or diabetes that develops over years.
Noncommunicable disease: A disease not passed from person to person, driven largely by behavioral, metabolic, and environmental risks.
Epidemiologic transition: The historical shift in leading causes of death from infectious to chronic diseases as populations live longer.
Actual causes of death: The behaviors and exposures, such as tobacco and poor diet, that underlie the diseases recorded as causes of death.
Risk factor: A characteristic or exposure that increases the likelihood of developing a disease.
Metabolic risk factors: Intermediate conditions such as high blood pressure, high blood sugar, obesity, and high cholesterol that lead to chronic disease.
Deaths of despair: Deaths from suicide, drug overdose, and alcohol, linked by Case and Deaton to declining economic and social conditions.

Environmental Health

Define environmental health and explain how the environment shapes human health.
Describe major environmental hazards, including air pollution, contaminated water, and toxic exposures.
Explain risk assessment and the disproportionate burden of environmental hazards.

The big picture

The air outdoors, the water from the tap, the food on the shelf, and the places where people live and work all shape their health. Environmental health is the branch of public health concerned with how the physical, chemical, and biological environment affects people, and with preventing the harm that environments can cause. Some of the largest health gains in history, from clean water to lead-free gasoline, came from environmental measures. This lesson defines environmental health, surveys the major hazards, and explains how public health assesses environmental risks and confronts the unequal way those risks fall across communities.

Key idea: Environmental health addresses how air, water, food, and place affect human health, and much of public health's success has come from making environments safer.

The environment as a determinant of health

Environmental exposures act on entire populations, often without any individual choice. Everyone downwind of a polluting plant is exposed to the same air, and everyone served by a water system shares its quality. The Lancet Commission on pollution and health, led by Landrigan and colleagues, estimated that pollution causes millions of deaths worldwide each year, more than many familiar diseases, with the heaviest toll in low-income countries. Environmental hazards also interact with social conditions, as poor housing brings both mold and lead. Because these exposures are collective and often invisible, they are a natural target for public health rather than for individual medical care.

Key idea: Environmental exposures affect whole populations regardless of individual choice, and pollution ranks among the largest causes of death worldwide.

Major environmental hazards

Several hazards dominate environmental health. Air pollution, both outdoor and indoor from cooking and heating fuels, contributes to heart and lung disease and premature death. Unsafe water and poor sanitation spread diarrheal disease, still a major killer of children globally. Toxic chemicals, including lead, mercury, pesticides, and industrial pollutants, damage the nervous system and other organs. Foodborne hazards cause illness through contamination. Climate change amplifies many of these, bringing heat waves, worsening air quality, shifting the range of diseases, and threatening food and water security. Each hazard calls for prevention at the source, such as cleaner fuels, safe water systems, and chemical regulation.

Key idea: Air pollution, unsafe water, toxic chemicals, foodborne hazards, and climate change are the major environmental threats, best addressed by prevention at the source.

The case of lead

Lead illustrates how environmental science drives policy. Lead is a potent neurotoxin with no safe level of exposure, especially harmful to the developing brains of young children. In a pooled international analysis, Lanphear and colleagues found that even blood lead levels well below old thresholds were linked to measurable loss of intellectual function. Evidence like this justified removing lead from gasoline and paint, decisions that sharply reduced children's blood lead levels across whole populations. Yet lead persists in old pipes, paint, and soil, as the Flint water crisis showed, so environmental health remains vigilant. The lead story shows prevention succeeding at the population scale.

Key idea: Lead has no safe level and harms children's brains, and evidence like Lanphear's drove population-wide policies that removed lead from gasoline and paint.

Risk assessment and regulation

To manage hazards, public health uses risk assessment, a structured way to estimate the danger a hazard poses. It identifies the hazard, estimates how much exposure people receive, judges the relationship between dose and response, and characterizes the overall risk. That assessment then informs risk management, the policy decisions and regulations that reduce exposure, often weighed against costs. Agencies such as the Environmental Protection Agency set standards for air and water on this basis. A guiding idea is the precautionary principle, which favors protective action when a serious hazard is plausible even before proof is complete, since waiting for certainty can cost lives.

Key idea: Risk assessment estimates the danger from a hazard and guides regulation, while the precautionary principle supports protective action before proof is complete.

Environmental justice

Environmental hazards do not fall evenly. Low-income communities and communities of color are more often located near highways, factories, waste sites, and polluted water, and they bear a heavier share of the resulting disease. This pattern is the focus of environmental justice, the principle that all people deserve equal protection from environmental harm and a fair voice in decisions that affect their environment. The Flint water crisis became a symbol of environmental injustice, where a majority-Black city was exposed to lead. Recognizing this uneven burden connects environmental health to the themes of equity that run through public health.

Key idea: Environmental hazards fall disproportionately on disadvantaged communities, and environmental justice seeks equal protection and a fair voice for all.

Common misconceptions

Environmental health is only about protecting nature. Its focus is how the environment affects human health, though the two are linked.
If a chemical is present, it must be causing harm. Risk depends on dose and exposure, which risk assessment is designed to estimate.
Lead poisoning was solved long ago. Lead persists in old pipes, paint, and soil, and crises like Flint show the danger remains.
Everyone faces the same environmental risks. Disadvantaged communities bear a disproportionate share, the concern of environmental justice.

Recap

Environmental health concerns how air, water, food, and place affect human health.
Environmental exposures act on whole populations, and pollution is a leading global killer.
Major hazards include air pollution, unsafe water, toxic chemicals, and climate change.
Risk assessment guides regulation, informed by the precautionary principle.
Environmental hazards fall unequally, the concern of environmental justice.

Sources

Landrigan, P. J., Fuller, R., Acosta, N. J. R., et al. (2018). The Lancet Commission on pollution and health. The Lancet, 391(10119), 462-512. doi.org/10.1016/S0140-6736(17)32345-0
Lanphear, B. P., Hornung, R., Khoury, J., et al. (2005). Low-level environmental lead exposure and children's intellectual function: An international pooled analysis. Environmental Health Perspectives, 113(7), 894-899. doi.org/10.1289/ehp.7688
Centers for Disease Control and Prevention. (n.d.). About the National Center for Environmental Health. cdc.gov
World Health Organization. (n.d.). Environmental health. who.int
U.S. Environmental Protection Agency. (n.d.). Health topics. epa.gov

Key terms
Environmental health: The branch of public health concerned with how the physical, chemical, and biological environment affects human health.
Air pollution: Harmful substances in outdoor or indoor air that contribute to heart and lung disease and premature death.
Toxic exposure: Contact with a harmful substance such as lead or mercury that can damage the nervous system or other organs.
Risk assessment: A structured process of estimating the danger a hazard poses, considering hazard, exposure, and dose-response.
Precautionary principle: The idea that protective action is justified when a serious hazard is plausible, even before proof is complete.
Environmental justice: The principle that all people deserve equal protection from environmental hazards and a fair voice in decisions.
Dose-response relationship: The link between the amount of an exposure and the size of its health effect, central to risk assessment.

Injury and Violence Prevention

Explain why injuries and violence are public health problems rather than accidents.
Apply the Haddon matrix to analyze and prevent injury.
Describe public health approaches to violence prevention.

The big picture

Injuries kill and disable millions of people each year, and for much of the last century they were dismissed as accidents, random misfortunes beyond control. Public health rejected that view. Injuries, whether from car crashes, falls, drownings, or violence, follow predictable patterns and are therefore preventable. Treating injury and violence as public health problems, not fate, has saved enormous numbers of lives, from seatbelts to safer roads. This lesson explains the public health approach to injury, introduces a classic tool for analyzing it, and extends the same prevention logic to violence.

Key idea: Injuries and violence are not random accidents but predictable, preventable public health problems that follow patterns science can address.

Injury as a public health problem

The word accident implies bad luck and no remedy. Public health replaced it with injury, an event whose causes can be studied and reduced. Injuries divide into unintentional, such as motor vehicle crashes, falls, poisonings, and drownings, and intentional, such as assault, suicide, and homicide. Together they are a leading cause of death, especially among the young, and they steal more years of potential life than many diseases because they strike early. Seeing injury as preventable opened the door to systematic action, and the results, such as the long decline in traffic deaths per mile driven, rank among public health's clearest successes.

Key idea: Reframing accidents as preventable injuries, both unintentional and intentional, allowed public health to reduce a leading cause of early death.

The Haddon matrix

William Haddon, a pioneer of injury prevention, offered a simple but powerful tool. The Haddon matrix crosses the three phases of an injury event, pre-event, event, and post-event, with three factors, the host or person, the agent or vehicle, and the environment. For a car crash, pre-event measures include driver sobriety and good brakes, event measures include seatbelts and airbags, and post-event measures include fast emergency care. The matrix shows that prevention is not only about changing behavior before a crash but also about reducing harm during and after it. This systems view shifted attention from blaming individuals to engineering safer conditions.

Key idea: The Haddon matrix analyzes injury across pre-event, event, and post-event phases and host, agent, and environment factors, revealing many points for prevention beyond individual behavior.

Passive protection and safer systems

A central insight of injury prevention is that passive protection, which works automatically without action by the individual, usually beats active measures that require constant effort. An airbag protects every occupant without being switched on, while a habit of careful driving must be sustained. Public health therefore favors changes to products and environments, such as child-resistant caps, guardrails, smoke detectors, and roads designed to forgive mistakes. The Safe System approach to road safety builds on this idea, accepting that people will err and designing streets, speeds, and vehicles so that human mistakes do not turn deadly. Engineering and policy often protect more than education alone.

Key idea: Passive, automatic protections built into products and environments prevent more injury than measures requiring constant individual effort.

Violence as a public health problem

Violence was long seen only as a matter for law enforcement, but public health treats it as a preventable health problem as well. In a landmark article, Mercy and colleagues laid out a public health approach to violence, defining the problem with data, identifying risk and protective factors, developing and testing prevention strategies, and scaling up what works. This approach addresses intimate partner violence, youth violence, child abuse, and suicide. Sampson, Morenoff, and Raudenbush showed that neighborhood conditions, including concentrated disadvantage and the collective willingness of neighbors to act, help explain differences in violence, pointing prevention toward communities and not only individuals.

Key idea: Public health treats violence as preventable, using data to identify risk and protective factors and addressing community conditions, not only individual offenders.

The public health approach in action

Injury and violence prevention follows the same four steps across problems: define the problem through surveillance, identify risk and protective factors, develop and evaluate interventions, and implement and scale those that work. Suicide prevention, for instance, combines means restriction such as safer medication packaging, crisis services, and responsible reporting. Overdose prevention combines naloxone distribution, safer prescribing, and treatment access. The common thread is prevention grounded in data and evaluation, targeting the conditions and environments that produce harm rather than relying on exhortation. This lesson closes the module by showing the prevention logic reaching even the problems once thought beyond public health.

Key idea: Injury and violence prevention applies a four-step, data-driven cycle, from defining the problem to scaling proven interventions, across causes from crashes to suicide.

Common misconceptions

Injuries are accidents that cannot be prevented. Injuries follow patterns and are preventable, which is why public health avoids the word accident.
Preventing injury just means telling people to be careful. Passive, engineered protections usually prevent more harm than education alone.
Violence is only a criminal justice issue. Public health treats violence as a preventable health problem with identifiable risk factors.
The Haddon matrix is only about the moment of the crash. It spans pre-event, event, and post-event phases, revealing many prevention points.

Recap

Injuries are predictable and preventable, not random accidents.
Injuries are unintentional or intentional and steal many years of early life.
The Haddon matrix analyzes injury across three phases and three factors.
Passive, automatic protections outperform measures needing constant effort.
Public health treats violence as preventable, addressing risk factors and community conditions.

Sources

Mercy, J. A., Rosenberg, M. L., Powell, K. E., Broome, C. V., & Roper, W. L. (1993). Public health policy for preventing violence. Health Affairs, 12(4), 7-29. doi.org/10.1377/hlthaff.12.4.7
Sampson, R. J., Morenoff, J. D., & Raudenbush, S. (2005). Social anatomy of racial and ethnic disparities in violence. American Journal of Public Health, 95(2), 224-232. doi.org/10.2105/AJPH.2004.037705
Centers for Disease Control and Prevention. (n.d.). Injury and violence prevention. cdc.gov
World Health Organization. (n.d.). Violence. who.int
World Health Organization. (n.d.). Injuries and violence. who.int

Key terms
Injury: Physical harm from an event whose causes can be studied and prevented, replacing the fatalistic term accident.
Unintentional injury: Injury without intent to harm, such as from motor vehicle crashes, falls, poisonings, or drownings.
Intentional injury: Injury resulting from purposeful violence, including assault, homicide, and suicide.
Haddon matrix: A framework crossing the pre-event, event, and post-event phases with host, agent, and environment factors to find prevention points.
Passive protection: Safety that works automatically without action by the individual, such as an airbag, generally more effective than active measures.
Safe System approach: A road safety strategy that designs streets, speeds, and vehicles so human mistakes do not cause death.
Public health approach to violence: A four-step method of defining the problem, identifying risk factors, developing interventions, and scaling what works.

Module 4: Promoting Health Across Populations

How public health moves from preventing disease to actively promoting health: the science of changing health behavior, the maternal and child health that anchors a society's wellbeing, and the global health that pursues equity across borders.

Health Behavior and Health Promotion

Explain why health behavior is central to public health and why it is hard to change.
Summarize major theories of health behavior, including the Health Belief Model and the stages of change.
Describe the socioecological model and the difference between health education and health promotion.

The big picture

Much of the disease burden in modern societies is tied to behavior: what people eat, whether they smoke, how active they are, and whether they seek care. Yet simply telling people to be healthier rarely works. Behavior is shaped by beliefs, habits, social networks, and the environments that make some choices easy and others hard. Public health draws on behavioral science to understand these forces and to design programs that help people change. This lesson surveys the main theories of health behavior and distinguishes narrow health education from the broader work of health promotion.

Key idea: Health behavior drives much modern disease, but changing it requires understanding the beliefs, habits, and environments behind behavior rather than simply urging people to do better.

Why behavior is hard to change

Knowledge alone seldom changes behavior. Most smokers know smoking is harmful, yet quitting is difficult. Behavior is anchored by habit, addiction, stress, social norms, and immediate rewards that outweigh distant risks. It is also constrained by circumstances, since a person cannot easily eat well in a neighborhood without a grocery store or exercise safely on streets without sidewalks. Behavioral science helps by identifying the specific beliefs and conditions that drive a behavior, so programs can target the right levers. The recurring lesson is that information is necessary but not sufficient, and that lasting change usually requires support and a supportive environment.

Key idea: Behavior resists change because habit, social norms, and circumstances outweigh knowledge, so effective programs address more than information.

The Health Belief Model

One of the oldest frameworks, the Health Belief Model developed by Rosenstock and colleagues, holds that people are more likely to take a health action when they believe they are susceptible to a serious threat, expect that the action will help, and see few barriers to it. A cue to action, such as a symptom or a reminder, can trigger the behavior, and confidence in one's ability, or self-efficacy, supports it. The model explains why a person may skip a screening they see as unlikely to matter, and it guides messages that raise perceived risk and benefit while lowering barriers.

Key idea: The Health Belief Model predicts action from perceived susceptibility, severity, benefits, and barriers, along with cues to action and self-efficacy.

Stages of change

People do not change all at once. The transtheoretical model, developed by Prochaska and DiClemente, describes change as a series of stages: precontemplation, not yet considering change; contemplation, weighing it; preparation, getting ready; action, making the change; and maintenance, sustaining it. Relapse is common and part of the process, not simply failure. The model's practical value is matching help to the stage. Someone in precontemplation needs information and motivation, while someone in action needs concrete support and relapse prevention. Meeting people where they are, rather than pushing everyone toward immediate action, makes behavior-change programs more effective.

Key idea: The stages of change model views behavior change as movement through precontemplation, contemplation, preparation, action, and maintenance, so help should match a person's stage.

The socioecological model

Individual theories are not enough, because behavior is nested in wider systems. The socioecological model arranges influences in layers: the individual, interpersonal relationships, organizations, the community, and public policy. A teenager's smoking is shaped by personal beliefs, friends and family, school rules, neighborhood advertising, and tobacco taxes all at once. The model directs public health to intervene at multiple levels rather than relying on individuals to resist an unhealthy environment. As Glanz and Bishop describe, using behavioral theory across these levels improves the design and results of interventions, moving beyond one-on-one persuasion.

Key idea: The socioecological model locates behavior within nested levels from the individual to policy, directing public health to act at several levels at once.

From health education to health promotion

Health education, the provision of information and skills, is one tool but not the whole job. Health promotion, defined by the World Health Organization, is the broader process of enabling people to increase control over and improve their health, combining education with policy, environmental change, and community action. The landmark Ottawa Charter set out actions such as building healthy public policy and creating supportive environments. Community-based participatory approaches, described by Wallerstein and Duran, involve communities as partners in designing programs, improving both relevance and trust. Health promotion thus unites individual behavior change with the structural changes that make healthy choices easier.

Key idea: Health promotion goes beyond health education, combining information with policy, environmental change, and community partnership to make healthy choices easier.

Common misconceptions

If people know the facts, they will act on them. Knowledge rarely suffices, because habit, norms, and circumstances also drive behavior.
Behavior change happens in a single decision. Models like the stages of change show it unfolds over time, with relapse a normal part.
Health promotion is just education. It combines education with policy, environmental change, and community action.
Bad health choices are simply personal failings. Choices are constrained by environments, which is why public health changes those environments.

Recap

Behavior drives much disease but resists change, because knowledge alone is not enough.
The Health Belief Model links action to perceived risk, benefits, and barriers.
The stages of change model matches help to a person's readiness.
The socioecological model locates behavior in nested levels from individual to policy.
Health promotion combines education with policy, environment, and community action.

Sources

Rosenstock, I. M. (1974). Historical origins of the Health Belief Model. Health Education Monographs, 2(4), 328-335. doi.org/10.1177/109019817400200403
Prochaska, J. O., & DiClemente, C. C. (1983). Stages and processes of self-change of smoking: Toward an integrative model of change. Journal of Consulting and Clinical Psychology, 51(3), 390-395. doi.org/10.1037/0022-006X.51.3.390
Glanz, K., & Bishop, D. B. (2010). The role of behavioral science theory in development and implementation of public health interventions. Annual Review of Public Health, 31, 399-418. doi.org/10.1146/annurev.publhealth.012809.103604
Wallerstein, N., & Duran, B. (2010). Community-based participatory research contributions to intervention research: The intersection of science and practice to improve health equity. American Journal of Public Health, 100(S1), S40-S46. doi.org/10.2105/AJPH.2009.184036
Rural Health Information Hub. (n.d.). Health promotion and disease prevention theories and models. ruralhealthinfo.org

Key terms
Health behavior: Actions that affect health, such as diet, physical activity, smoking, and seeking care.
Health Belief Model: A theory predicting health action from perceived susceptibility, severity, benefits, barriers, cues, and self-efficacy.
Self-efficacy: A person's confidence in their ability to carry out a specific behavior, which supports change.
Transtheoretical model: A model describing behavior change as movement through precontemplation, contemplation, preparation, action, and maintenance.
Socioecological model: A framework placing behavior within nested levels from the individual through relationships and community to policy.
Health education: The provision of information and skills intended to support healthy behavior.
Health promotion: The broad process of enabling people to increase control over and improve their health, combining education with policy and environmental change.

Maternal, Child, and Reproductive Health

Explain why maternal and child health are central indicators of a population's health.
Describe key measures such as infant and maternal mortality and their determinants.
Summarize public health approaches across the reproductive and early-life span.

The big picture

The health of mothers and children is often called the foundation of public health, and their death rates are among the most sensitive indicators of how well a society is doing. Pregnancy, birth, and early childhood are periods of both vulnerability and opportunity, when public health action yields lifelong returns. This field, known as maternal and child health, covers reproductive health, pregnancy and birth, infancy, and child development. This lesson explains why these measures matter, what drives them, and how public health protects health across the reproductive and early-life span.

Key idea: Maternal and child health are foundational indicators of a population's wellbeing, and early-life investment yields lifelong returns.

Why these measures matter

Infant and maternal mortality reflect far more than medical care. They capture nutrition, sanitation, education, the status of women, and the strength of health systems, which is why they are used to compare the health of whole nations. A high infant mortality rate signals problems reaching well beyond hospitals into housing, income, and food. Wise showed that disparities in infant mortality trace to social and economic conditions, not biology alone. Because these outcomes are so sensitive to the conditions of life, improving them tends to require broad social investment, and tracking them reveals inequities that averages can hide.

Key idea: Infant and maternal mortality are sensitive indicators of a whole society's conditions, reflecting nutrition, education, and equity far beyond medical care.

Key measures

Several measures anchor the field. The infant mortality rate counts deaths before age one per 1,000 live births. The maternal mortality ratio counts maternal deaths per 100,000 live births, and it remains strikingly high in many countries and unequal within wealthy ones. Low birth weight and preterm birth predict later problems. The under-five mortality rate is a key global indicator. In the United States, large racial disparities persist, with Black women facing much higher maternal and infant mortality than white women, gaps that are not explained by income alone and point to systemic factors including the effects of racism on health.

Key idea: Infant mortality, maternal mortality, and birth weight are core measures, and persistent racial disparities in them point to systemic causes beyond income.

Reproductive health

Reproductive health spans the ability to have a safe and satisfying reproductive life, including family planning, prevention and treatment of sexually transmitted infections, and safe pregnancy and childbirth. Access to contraception allows people to plan the timing and number of pregnancies, which improves maternal and child outcomes and expands opportunities. Preventing and treating sexually transmitted infections protects fertility and prevents transmission to newborns. Public health also promotes comprehensive education and screening. Reproductive health is shaped by law, culture, and access, and gaps in it fall hardest on those with the fewest resources, making it a persistent equity concern.

Key idea: Reproductive health includes family planning, sexually transmitted infection control, and safe pregnancy, and access to it strongly shapes maternal and child outcomes and equity.

The early-life span and prevention

Public health protects health across a continuum. Before and during pregnancy, prenatal care, good nutrition including folic acid to prevent birth defects, and avoiding tobacco and alcohol support healthy development. At birth, skilled care and newborn screening catch problems early. In infancy and childhood, breastfeeding support, immunization, safe sleep to prevent sudden infant death, injury prevention, and developmental screening build a healthy start. Barker's research suggested that conditions in the womb and early life influence the risk of chronic disease decades later, an idea known as the developmental origins of health and disease. Early investment therefore pays off across the entire life course.

Key idea: Public health acts across the early-life continuum from prenatal care through childhood, and early conditions shape health decades later.

Programs and systems

The United States supports maternal and child health through programs such as the Maternal and Child Health services block grant administered by the Health Resources and Services Administration, nutrition support like the WIC program, and home visiting for new parents. Globally, the reduction of child mortality has been one of the great successes of recent decades, driven by vaccines, oral rehydration for diarrhea, better nutrition, and skilled birth attendance, though progress on maternal mortality has lagged. These programs show public health working across sectors, since healthy mothers and children require not only clinics but income support, nutrition, and safe environments.

Key idea: Maternal and child health relies on programs spanning clinical care, nutrition, and home visiting, and global child mortality has fallen sharply through a handful of proven interventions.

Common misconceptions

Infant mortality just measures the quality of hospitals. It reflects nutrition, sanitation, education, and equity across the whole society.
Maternal deaths are rare and unavoidable. Many are preventable, and rates remain high and unequal, including large racial gaps in wealthy countries.
Racial disparities in birth outcomes are explained by income. Gaps persist across income levels and point to systemic factors including racism.
Child health is only about medical care. Nutrition, immunization, safe environments, and early development all shape it.

Recap

Maternal and child health are foundational, sensitive indicators of a society's conditions.
Infant and maternal mortality reflect far more than medical care.
Reproductive health, including family planning, strongly shapes maternal and child outcomes.
Public health acts across the early-life continuum, and early conditions shape later health.
Programs span clinical care, nutrition, and home visiting, and global child mortality has fallen sharply.

Sources

Wise, P. H. (2003). The anatomy of a disparity in infant mortality. Annual Review of Public Health, 24, 341-362. doi.org/10.1146/annurev.publhealth.24.100901.140816
Barker, D. J. P. (1990). The fetal and infant origins of adult disease. BMJ, 301(6761), 1111. doi.org/10.1136/bmj.301.6761.1111
Centers for Disease Control and Prevention. (n.d.). Reproductive health. cdc.gov
Health Resources and Services Administration. (n.d.). Maternal and Child Health Bureau. mchb.hrsa.gov
World Health Organization. (n.d.). Maternal health. who.int

Key terms
Maternal and child health: The field of public health focused on the health of women, mothers, infants, and children, including reproductive health.
Infant mortality rate: The number of deaths before age one per 1,000 live births, a key indicator of population health.
Maternal mortality ratio: The number of maternal deaths per 100,000 live births, reflecting the safety of pregnancy and childbirth.
Reproductive health: The capacity for a safe and satisfying reproductive life, including family planning and prevention of sexually transmitted infections.
Prenatal care: Health care during pregnancy that supports the health of the pregnant person and the developing fetus.
Low birth weight: A birth weight below a defined threshold that predicts higher risk of health problems in infancy and later.
Developmental origins of health and disease: The idea, associated with Barker, that conditions in the womb and early life influence chronic disease risk in adulthood.

Global Health

Define global health and distinguish it from international and public health.
Describe the global burden of disease and how it varies by country income.
Explain major global health actors, goals, and challenges.

The big picture

Health does not stop at borders. A pathogen can circle the globe in a day, and the causes and solutions of ill health are shared across nations. Global health is the area of study and practice that places a priority on improving health and achieving health equity for all people worldwide. It grew out of older fields of tropical and international health but focuses on problems that transcend borders and on fairness between rich and poor countries. This lesson defines global health, describes how the burden of disease differs across the world, and introduces the actors, goals, and debates that shape the field.

Key idea: Global health seeks to improve health and health equity for all people worldwide, addressing problems and inequities that cross national borders.

What global health is

Global health is often distinguished from related terms. International health traditionally referred to health work in low-income countries, framed as aid from rich to poor. Public health addresses population health within a society. Global health blends both, focusing on health issues that transcend borders, such as pandemics, tobacco, and climate, and emphasizing equity and shared responsibility rather than one-way charity. It is inherently multidisciplinary, drawing on medicine, economics, policy, and the social sciences. A guiding principle is that health is a shared global concern, so a disease outbreak or a shortage of health workers anywhere can affect people everywhere.

Key idea: Global health addresses cross-border health problems with an emphasis on equity and shared responsibility, distinct from one-directional international aid.

The global burden of disease

The Global Burden of Disease studies measure health worldwide using combined metrics such as the disability-adjusted life year, which counts both years lost to early death and years lived with disability. The patterns reveal an epidemiologic transition in progress. Low-income countries still bear heavy burdens of infectious diseases, maternal and child conditions, and malnutrition, while noncommunicable diseases dominate in richer countries and rise quickly in poorer ones. The Lim and colleagues risk-factor analysis showed that a mix of dietary, metabolic, environmental, and behavioral risks drives much of this burden. Mapping the burden guides where the world directs attention and resources.

Key idea: The Global Burden of Disease studies show low-income countries facing infectious and maternal conditions while noncommunicable diseases rise everywhere, guiding global priorities.

Determinants and inequity between nations

The vast gaps in health between countries stem from the same determinants that operate within them, magnified. Poverty, weak health systems, limited education, poor sanitation, and political instability drive much of the difference, and Marmot's Commission on Social Determinants of Health argued that these conditions, and the inequities behind them, are the fundamental causes of global ill health. A shortage of health workers, sometimes worsened when trained professionals migrate to wealthier countries, further weakens systems. Addressing global health therefore means more than delivering medicine. It requires strengthening the social and economic conditions and systems that produce health.

Key idea: Health gaps between nations arise from social and economic determinants magnified by poverty and weak systems, so global health requires strengthening conditions, not only delivering care.

Actors, goals, and financing

Many actors shape global health. The World Health Organization coordinates and sets norms. Other players include national governments and agencies, the World Bank, global funds for specific diseases, foundations, and nongovernmental organizations. Shared goals have focused effort, first the Millennium Development Goals and now the Sustainable Development Goals, whose third goal aims to ensure healthy lives and wellbeing for all at all ages. Jamison and colleagues argued in Global Health 2035 that a grand convergence in health, bringing the poorest countries up to the levels of better-off ones, is achievable within a generation with sufficient investment. Financing and coordination remain central challenges.

Key idea: Global health is shaped by the WHO and many other actors pursuing shared goals like the Sustainable Development Goals, with financing and coordination as central challenges.

Global health security

Recent decades have underscored global health security, the effort to prevent, detect, and respond to health threats that cross borders. Outbreaks of SARS, Ebola, and above all COVID-19 revealed how quickly disease spreads and how unequally the world is prepared. Weak surveillance and health systems anywhere become everyone's risk, and vaccines and supplies are often distributed unequally during crises. Climate change and antimicrobial resistance add long-term threats. The lesson of the pandemic era is that investing in health systems, surveillance, and equity worldwide is not charity but collective self-protection, a theme that leads into the preparedness discussed later in this course.

Key idea: Global health security recognizes that cross-border threats like pandemics make investment in health systems and equity worldwide a matter of collective protection.

Common misconceptions

Global health means charity from rich countries to poor ones. Modern global health emphasizes equity, shared responsibility, and problems that cross all borders.
Poor countries only face infectious disease. Noncommunicable diseases are rising rapidly in low- and middle-income countries.
Global health is only about delivering medicine. It also requires strengthening the social conditions and health systems that produce health.
A distant outbreak is not our concern. Diseases cross borders quickly, so weak systems anywhere pose a risk everywhere.

Recap

Global health seeks health and equity worldwide for problems that cross borders.
The Global Burden of Disease shows shifting patterns across country income levels.
Health gaps between nations stem from social and economic determinants magnified.
The WHO and many actors pursue shared goals such as the Sustainable Development Goals.
Global health security treats worldwide investment as collective self-protection.

Sources

Jamison, D. T., Summers, L. H., Alleyne, G., et al. (2013). Global health 2035: A world converging within a generation. The Lancet, 382(9908), 1898-1955. doi.org/10.1016/S0140-6736(13)62105-4
Marmot, M., Friel, S., Bell, R., Houweling, T. A. J., & Taylor, S. (2008). Closing the gap in a generation: Health equity through action on the social determinants of health. The Lancet, 372(9650), 1661-1669. doi.org/10.1016/S0140-6736(08)61690-6
Lim, S. S., Vos, T., Flaxman, A. D., et al. (2012). A comparative risk assessment of burden of disease and injury attributable to 67 risk factors, 1990-2010. The Lancet, 380(9859), 2224-2260. doi.org/10.1016/S0140-6736(12)61766-8
World Health Organization. (n.d.). Global Health Observatory. who.int
United Nations. (n.d.). Sustainable Development Goal 3: Good health and well-being. sdgs.un.org

Key terms
Global health: The study and practice of improving health and achieving health equity for all people worldwide, focused on cross-border issues.
International health: An older term for health work in low-income countries, often framed as aid from wealthier nations.
Global Burden of Disease: A large ongoing study measuring death and disability worldwide using metrics such as the disability-adjusted life year.
Disability-adjusted life year: A measure combining years of life lost to early death with years lived with disability.
Sustainable Development Goals: A set of global goals adopted in 2015, the third of which targets health and wellbeing for all at all ages.
Grand convergence: Jamison and colleagues' vision of bringing the poorest countries' health up to the level of better-off ones within a generation.
Global health security: The effort to prevent, detect, and respond to health threats that cross national borders.

Module 5: Systems, Policy, and Ethics

The systems and rules that carry public health forward: the organization, financing, and economics of health systems, the preparedness and response that meet emergencies, and the ethics and law that justify and limit public action.

Health Policy, Systems, and Financing

Describe the building blocks of a health system and how the United States system is organized.
Explain how health care is financed and the difference between public and private coverage.
Apply basic health economics concepts, including externalities, cost-effectiveness, and market failure.

The big picture

Public health does not operate in a vacuum. It works within health systems shaped by policy and paid for through complex financing, and it competes for limited resources. Understanding how health systems are organized, how they are financed, and how economists think about health helps explain why some countries achieve better health at lower cost than others. This lesson introduces the building blocks of a health system, the way the United States finances care, and the core ideas of health economics that inform public health decisions about where to spend scarce dollars for the greatest gain.

Key idea: Public health operates within health systems and budgets, so understanding health system organization, financing, and economics is essential to improving health.

Building blocks of a health system

The World Health Organization describes a health system through building blocks: service delivery, the health workforce, information systems, access to medicines and technologies, financing, and leadership and governance. A strong system needs all of them working together. Systems also pursue several goals at once, often summarized as the Triple Aim: better health for populations, better care experience for individuals, and lower cost, to which many add a fourth aim of workforce wellbeing. These blocks and aims give a common language for comparing systems and diagnosing where one is failing, whether from too few workers, weak data, or unstable financing.

Key idea: A health system rests on building blocks such as workforce, information, medicines, and financing, and it pursues better health, better care, and lower cost together.

The United States health system

The United States health system is a mix of private and public arrangements without a single unified structure. Most working-age people get private insurance through employers, while government programs cover others: Medicare for people over sixty-five and some with disabilities, Medicaid for many with low incomes, and separate programs for veterans and children. Despite spending far more per person than any other nation, the United States has worse outcomes on measures such as life expectancy and infant mortality than many peers. Schroeder argued that this gap reflects underinvestment in the behavioral and social determinants of health rather than a shortage of medical care.

Key idea: The United States relies on a mix of private and public coverage and spends the most per person, yet achieves worse outcomes than many peers, reflecting underinvestment in determinants.

Financing health care

Health care is paid for in several ways. In tax-funded systems, government collects taxes and funds care for all. In social insurance systems, mandatory contributions pool risk. In private insurance, people or employers buy coverage. Most countries blend these. Insurance exists because health costs are unpredictable and can be catastrophic, so pooling risk across many people protects each from ruin. A recurring policy goal is universal health coverage, ensuring everyone can obtain needed care without financial hardship. How a system is financed shapes who is covered, what is covered, and how providers are paid, which in turn affects both cost and equity.

Key idea: Health care is financed through taxes, social insurance, and private insurance, all pooling unpredictable risk, and financing choices shape coverage, cost, and equity.

Health economics: scarcity and value

Health economics studies how scarce resources are allocated to produce health. Because no system can afford everything, choices are unavoidable, and economics offers tools to make them well. Cost-effectiveness analysis compares the cost of an intervention with the health it produces, often measured in quality-adjusted life years, so that a fixed budget yields the most health. As Weinstein and Stason explained, this lets decision makers compare very different options on a common footing. The concept of opportunity cost is central. Every dollar spent on one program is a dollar not available for another, so the real cost of a choice is the best alternative given up.

Key idea: Health economics uses tools like cost-effectiveness analysis and the idea of opportunity cost to allocate scarce resources for the greatest health gain.

Why health markets fail

Health care does not behave like an ordinary market, which is a core reason for public involvement. Information is unequal, since patients cannot easily judge what care they need. Insurance adds further complications. Above all, many public health goods create externalities, effects on others not captured in a private transaction. A vaccination protects not only the recipient but everyone around them, so individuals left to themselves tend to buy too little of it. Clean air and disease surveillance are public goods that markets underprovide. These market failures justify collective action through government, explaining why public health is a public responsibility rather than a private purchase.

Key idea: Health markets fail through unequal information, externalities, and public goods, which is why public health requires collective action rather than private markets alone.

Common misconceptions

Spending more on health care always means better health. The United States spends the most yet lags peers, because outcomes depend heavily on determinants beyond care.
Health care is a market like any other. Unequal information, externalities, and public goods make it fail as an ordinary market.
Cost-effectiveness means simply choosing the cheapest option. It compares cost to health produced, seeking the most health per dollar, not the lowest price.
Vaccination is a purely private benefit. It creates positive externalities by protecting others, so markets underprovide it.

Recap

Health systems rest on building blocks and pursue better health, better care, and lower cost.
The United States mixes private and public coverage, spends the most, yet lags on outcomes.
Health care is financed through taxes, social insurance, and private insurance that pool risk.
Health economics uses cost-effectiveness and opportunity cost to allocate scarce resources.
Market failures from externalities and public goods justify collective public health action.

Sources

Weinstein, M. C., & Stason, W. B. (1977). Foundations of cost-effectiveness analysis for health and medical practices. New England Journal of Medicine, 296(13), 716-721. doi.org/10.1056/NEJM197703312961304
Schroeder, S. A. (2007). We can do better: Improving the health of the American people. New England Journal of Medicine, 357(12), 1221-1228. doi.org/10.1056/NEJMsa073350
KFF. (n.d.). Health policy research, polling, and news. kff.org
Centers for Medicare & Medicaid Services. (n.d.). CMS.gov ↗. cms.gov
World Health Organization. (n.d.). Health financing. who.int
Commonwealth Fund. (n.d.). International health system profiles. commonwealthfund.org

Key terms
Health system: The organizations, people, and resources whose primary purpose is to promote, restore, and maintain health.
Universal health coverage: The goal that all people can obtain needed health services without suffering financial hardship.
Social insurance: A financing model in which mandatory contributions pool risk to fund health care for members.
Cost-effectiveness analysis: A method comparing the cost of an intervention with the health it produces, often in quality-adjusted life years.
Opportunity cost: The value of the best alternative given up when a resource is used for one purpose rather than another.
Externality: An effect of a transaction on people not party to it, such as the protection others gain from one person's vaccination.
Public good: A good, such as clean air or disease surveillance, that markets underprovide because its benefits are shared and nonexclusive.

Public Health Preparedness and Emergency Response

Define public health emergency preparedness and its core capabilities.
Describe the emergency management cycle and the incident command structure.
Explain risk communication and lessons from recent public health emergencies.

The big picture

Floods, hurricanes, pandemics, chemical spills, and bioterrorism all threaten health suddenly and at scale, and they test whether a public health system can respond. Public health emergency preparedness is the capacity to prevent, protect against, quickly respond to, and recover from health emergencies. Unlike routine work, emergencies demand rapid coordination across agencies under uncertainty. The COVID-19 pandemic showed both the value of preparedness and the cost of gaps in it. This lesson defines preparedness, describes how emergencies are managed, and explains the risk communication that can determine whether the public trusts and follows guidance.

Key idea: Public health emergency preparedness is the capacity to prevent, respond to, and recover from sudden large-scale threats to health, demanding rapid coordination under uncertainty.

What preparedness means

Nelson and colleagues defined public health emergency preparedness as the ability of the health system and community to prevent, protect against, quickly respond to, and recover from emergencies, particularly those whose scale exceeds routine capacity. Preparedness is built in advance through planning, training, exercises, stockpiles, and surveillance, not improvised during a crisis. Public health agencies organize this work around defined capabilities, such as surveillance and epidemiological investigation, laboratory testing, mass vaccination or medication distribution, and coordination with hospitals. The aim is a system that can surge, expanding rapidly when demand spikes, then return to normal, all while continuing essential everyday services.

Key idea: Preparedness is capacity built in advance through planning, training, stockpiles, and defined capabilities so a system can surge during an emergency and recover afterward.

The emergency management cycle

Emergency management is often described as a cycle with four phases. Mitigation reduces the risk and impact of hazards before they occur, such as levees against floods or strong routine vaccination. Preparedness builds plans, supplies, and skills. Response is the immediate action during an emergency to save lives and limit harm. Recovery restores health, services, and normal life afterward, and offers a chance to rebuild more safely. The phases repeat and overlap, and lessons from recovery feed back into mitigation for the next event. Thinking in phases keeps attention on prevention and long-term resilience, not only on the dramatic response.

Key idea: The emergency management cycle of mitigation, preparedness, response, and recovery keeps focus on reducing risk and building resilience, not only on the immediate crisis.

Coordinating a response

Large emergencies involve many agencies that must work as one. To avoid chaos, responders use the Incident Command System, a standardized structure that assigns clear roles, a single chain of command, and common terminology so that police, fire, health, and other agencies can coordinate. Public health has specific roles within it, from running surveillance to distributing countermeasures from national stockpiles. Coordination also crosses levels of government, with local, state, and federal authorities each holding responsibilities, and with agencies such as the Administration for Strategic Preparedness and Response and the Centers for Disease Control and Prevention supporting states. Clear structure lets a response scale without collapsing into confusion.

Key idea: Emergencies are coordinated through the standardized Incident Command System and across levels of government, giving many agencies clear roles and a single chain of command.

Risk communication

In an emergency, what officials say and how they say it can matter as much as the medical response. Risk communication is the exchange of information with the public about a threat, aiming to inform decisions and maintain trust. As Reynolds and Seeger describe, good practice is to be first, be right, and be credible, to acknowledge uncertainty honestly, and to express empathy rather than issue commands. Poor communication, whether overreassuring, contradictory, or dismissive of public concern, erodes trust and compliance. The COVID-19 pandemic, marked by shifting guidance and misinformation, showed how fragile trust can be and how central clear, honest communication is to an effective response.

Key idea: Risk communication that is early, accurate, honest about uncertainty, and empathetic sustains the public trust on which an effective emergency response depends.

Lessons from recent emergencies

Recent emergencies have taught hard lessons. Pandemics such as COVID-19 revealed gaps in surveillance, supply chains, surge capacity, and the fair distribution of vaccines, and showed how deeply emergencies widen existing inequities, striking hardest at those already disadvantaged. Hurricanes and heat waves, worsened by climate change, exposed the vulnerability of people who depend on power for medical equipment or lack the means to evacuate. A recurring theme is that preparedness and equity are linked, because a response that ignores vulnerable groups fails. Preparedness is therefore not a separate specialty but an extension of everyday public health into moments of crisis.

Key idea: Recent emergencies show that gaps in surveillance, supplies, and equity determine outcomes, and that preparedness must protect the most vulnerable to succeed.

Common misconceptions

Preparedness can be improvised when a crisis hits. It is built in advance through planning, training, stockpiles, and surveillance.
Emergency management is only about the response phase. It is a cycle that also includes mitigation, preparedness, and recovery.
In a crisis, officials should project total certainty. Honest acknowledgment of uncertainty builds more durable trust than false reassurance.
Emergencies affect everyone equally. They typically strike hardest at already disadvantaged groups, so equity is central to preparedness.

Recap

Preparedness is the capacity to prevent, respond to, and recover from health emergencies.
It is built in advance through planning, capabilities, and the ability to surge.
The emergency management cycle spans mitigation, preparedness, response, and recovery.
The Incident Command System coordinates many agencies under one clear structure.
Honest risk communication and attention to equity are central to effective response.

Sources

Nelson, C., Lurie, N., Wasserman, J., & Zakowski, S. (2007). Conceptualizing and defining public health emergency preparedness. American Journal of Public Health, 97(Suppl 1), S9-S11. doi.org/10.2105/AJPH.2007.114496
Reynolds, B., & Seeger, M. W. (2005). Crisis and emergency risk communication as an integrative model. Journal of Health Communication, 10(1), 43-55. doi.org/10.1080/10810730590904571
Centers for Disease Control and Prevention. (n.d.). Office of Readiness and Response. cdc.gov
Administration for Strategic Preparedness and Response. (n.d.). ASPR. aspr.gov
World Health Organization. (n.d.). Health emergencies: What we do. who.int

Key terms
Public health emergency preparedness: The capacity to prevent, protect against, quickly respond to, and recover from health emergencies exceeding routine capacity.
Mitigation: Actions taken before a hazard to reduce its risk and impact, such as levees or routine vaccination.
Surge capacity: The ability of a health system to expand rapidly to meet a sharp increase in demand during an emergency.
Emergency management cycle: The recurring phases of mitigation, preparedness, response, and recovery used to manage hazards.
Incident Command System: A standardized structure assigning clear roles and a single chain of command so agencies can coordinate a response.
Risk communication: The exchange of information with the public about a threat to inform decisions and maintain trust.
Resilience: The ability of a community or system to withstand a shock and recover its functioning afterward.

Ethics and Law in Public Health

Explain why public health raises distinctive ethical questions beyond clinical ethics.
Describe key ethical principles and frameworks for public health.
Summarize the legal foundations and limits of public health authority.

The big picture

Public health often acts on whole populations, and sometimes it limits individual freedom for the common good, as when it quarantines the exposed, requires vaccination for school, or bans smoking indoors. These powers raise hard ethical and legal questions that clinical medicine, focused on a consenting patient, rarely faces. When is it justified to override individual liberty to protect the public? Who decides, and within what legal limits? This lesson explains why public health ethics differs from clinical ethics, introduces frameworks for making such judgments, and outlines the legal foundations and constraints of public health authority.

Key idea: Because public health acts on populations and can limit individual freedom for the common good, it raises distinctive ethical and legal questions beyond those of clinical care.

Why public health ethics is distinctive

Clinical ethics centers on the individual patient, guided by principles such as respecting autonomy, doing good, avoiding harm, and treating people fairly. Public health ethics keeps these but adds a population perspective, weighing collective benefit against individual rights. It routinely faces tensions clinical care avoids: the good of the community against personal liberty, prevention that burdens many to help a few, and the fair distribution of both benefits and burdens. Kass proposed an ethics framework asking what a program's goals are, how effective it is, what burdens it imposes, whether those burdens are fairly distributed, and whether they can be minimized. Such questions structure public health's characteristic trade-offs.

Key idea: Public health ethics extends clinical principles to populations, weighing collective benefit against individual liberty and the fair distribution of benefits and burdens.

Core principles and frameworks

Several ideas recur in public health ethics. The harm principle, from John Stuart Mill, holds that limiting a person's liberty is most justified to prevent harm to others, which supports measures against contagion. Proportionality asks that a restriction be no greater than necessary to achieve its aim. Transparency and public justification require that reasons be given openly. Attention to equity demands that the disadvantaged not bear unfair burdens. Childress and colleagues mapped this terrain, identifying justifying conditions for coercive measures, including effectiveness, proportionality, necessity, least infringement, and public justification. These frameworks do not give automatic answers, but they discipline the reasoning behind difficult decisions.

Key idea: Public health ethics draws on the harm principle, proportionality, transparency, and equity, and frameworks like Childress and colleagues set conditions that justify coercive measures.

The legal foundation of public health

Public health authority rests on law. In the United States, the police power reserved to the states gives them broad authority to protect health, safety, and welfare, which is the basis for vaccination requirements, quarantine, sanitation rules, and licensing. The Supreme Court affirmed this in Jacobson v. Massachusetts in 1905, upholding a mandatory smallpox vaccination law and ruling that individual liberty may be reasonably restrained to protect the community from a serious threat. Federal authority also plays a role, especially over interstate and foreign matters through the power to regulate commerce. Local health departments carry out much of the day-to-day legal work of public health.

Key idea: Public health authority in the United States rests largely on the states' police power, affirmed in Jacobson v. Massachusetts, which allows reasonable limits on liberty to protect the community.

Limits on public health power

Public health power is broad but not unlimited. Constitutional rights, including due process and equal protection, constrain how far the state may go, and courts have grown more protective of individual liberty since 1905. Measures must generally be reasonable, not arbitrary, and increasingly must use the least restrictive means that will achieve the goal. History supplies warnings, as public health powers have been abused to justify discrimination and coercion, from the segregation of the sick to the unethical Tuskegee syphilis study. These abuses spurred stronger protections for research participants and greater attention to justice. Sound public health law balances effective protection with respect for rights.

Key idea: Public health power is limited by constitutional rights and the requirement to use reasonable, least-restrictive means, and past abuses drive today's stronger protections.

Ethics in practice

Ethical and legal questions arise constantly in practice. Mandatory reporting of diseases must be balanced against privacy. Screening programs weigh early detection against the harms of false results. Emergency powers must be strong enough to act yet restrained enough to protect rights. Allocating scarce resources, such as vaccines in a pandemic, demands fair criteria decided openly. The recurring task is to justify public action in terms the community can accept, grounded in evidence, proportionate to the threat, transparent about reasons, and attentive to those most affected. Ethics and law are therefore not obstacles to public health but part of how it earns and keeps public trust.

Key idea: In practice, public health continually balances effectiveness against rights through evidence, proportionality, transparency, and fairness, which is how it earns public trust.

Common misconceptions

Public health ethics is the same as clinical ethics. It adds a population perspective, weighing collective benefit against individual rights.
Public health can do whatever it judges necessary. Its power is limited by constitutional rights and the requirement of reasonable, least-restrictive means.
Jacobson v. Massachusetts gives unlimited power to compel. It upheld reasonable measures against a serious threat, not unlimited authority, and later rulings added protections.
Ethics just slows public health down. Ethical and legal justification is how public health earns the trust that makes action possible.

Recap

Public health ethics extends clinical principles to populations and their trade-offs.
Frameworks weigh effectiveness, proportionality, necessity, least infringement, and equity.
United States public health authority rests largely on the states' police power.
Jacobson v. Massachusetts affirmed reasonable limits on liberty to protect the community.
Constitutional rights and past abuses set real limits on public health power.

Sources

Kass, N. E. (2001). An ethics framework for public health. American Journal of Public Health, 91(11), 1776-1782. doi.org/10.2105/AJPH.91.11.1776
Childress, J. F., Faden, R. R., Gaare, R. D., Gostin, L. O., Kahn, J., Bonnie, R. J., ... & Nieburg, P. (2002). Public health ethics: Mapping the terrain. Journal of Law, Medicine & Ethics, 30(2), 170-178. doi.org/10.1111/j.1748-720X.2002.tb00384.x
Legal Information Institute. (n.d.). Jacobson v. Massachusetts, 197 U.S. 11 (1905). Cornell Law School. law.cornell.edu
Centers for Disease Control and Prevention. (n.d.). Public health ethics. cdc.gov
Centers for Disease Control and Prevention. (n.d.). Public Health Law Program. cdc.gov

Key terms
Public health ethics: The field weighing collective benefit against individual rights in decisions affecting the health of populations.
Harm principle: Mill's principle that restricting a person's liberty is most justified to prevent harm to others.
Proportionality: The requirement that a public health restriction be no greater than necessary to achieve its aim.
Police power: The authority reserved to the states to protect the health, safety, and welfare of the public.
Jacobson v. Massachusetts: The 1905 Supreme Court case upholding a mandatory vaccination law and reasonable limits on liberty to protect the community.
Least restrictive means: The principle that public health should achieve its goal with the smallest possible infringement on liberty.
Due process: The constitutional guarantee of fair procedures that constrains how the state may exercise public health power.

Introduction to Public Health

Module 1: Foundations of Public Health

What Is Public Health?

The big picture

A population, not a patient

Public health and medicine compared

The prevention framework

Population thinking and the prevention paradox

Why public health is often invisible

Common misconceptions

Recap

Sources

The History, Core Functions, and Essential Services of Public Health

The big picture

From miasma to microbes

The twentieth century and beyond

Three core functions

The ten essential public health services

Infrastructure and the health impact pyramid

Common misconceptions

Recap

Sources

Determinants of Health and Health Equity

The big picture

What determines health

The social determinants of health

The social gradient

Disparities, inequities, and equity

Acting on the determinants

Common misconceptions

Recap

Sources

Module 2: Epidemiology and Data in Public Health

Epidemiology: Measuring Health and Disease

The big picture

What epidemiology is

Counts, ratios, proportions, and rates

Incidence and prevalence

Measuring death and burden

Comparing populations fairly

Common misconceptions

Recap

Sources

Study Designs and Causal Inference

The big picture

Descriptive and observational designs

Experiments and the randomized trial

Association is not causation

The Bradford Hill considerations

A worked example: smoking and lung cancer

Common misconceptions

Recap

Sources

Biostatistics and Data in Public Health

The big picture

Describing data: center and spread

From sample to population: uncertainty

Significance and its limits

Public health surveillance

Sources of data and their limits

Common misconceptions

Recap

Sources

Module 3: Preventing Disease and Injury

Infectious Disease and Outbreak Investigation

The big picture

The chain of infection

Herd immunity

Strategies to control infectious disease

Steps of an outbreak investigation

Emerging and re-emerging threats

Common misconceptions

Recap

Sources

Chronic Disease Prevention

The big picture

The epidemiologic transition

Actual causes of death

Shared risk factors

Population strategies for prevention