What Is Epidemiology?

Some call it a science and some say it’s more like journalism. Its practitioners have backgrounds in diverse areas. They work in offices and labs, on college campuses, in community health centers and all over the world. It’s a term we encounter a lot in the news lately, but exactly what is epidemiology?

The word epidemiology comes from three Greek words: epi (on or upon), demos (people), logos (the study of). The word has its roots in the study of what befalls a population.¹

The Dictionary of Epidemiology provides this definition:

“Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.”²

The Centers for Disease Control and Prevention (CDC) highlights several specifics within that definition:

“Epidemiology is the study (scientific, systematic, and data-driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (neighborhood, school, city, state, country, global). It is also the application of this study to the control of health problems.”³

The CDC goes on to say that epidemiology is “the method used to find the causes of health outcomes and diseases in populations.”³ That is, the community as a whole is viewed as the patient, and individuals are viewed collectively.

The focus, then, is on sources of collective suffering—environmental exposures, infectious and non-infectious diseases, injuries, natural disasters, terrorism, and so on. In this way, epidemiology is tied directly to public health.

The American College of Epidemiology, the professional organization for epidemiologists in this country, notes that, “Over the past three decades, epidemiology has matured into a field of its own, as both an academic discipline and a field of practice in a large variety of health agencies, hospitals, and research institutions. The past twenty years have been marked by a significant increase in the number of individuals who have chosen epidemiology as a career or who have entered epidemiology from such disciplines as medicine, statistics, sociology, genetics and biology.”⁴

So what do epidemiologists do? Often called ‘disease detectives,’ they search for the causes of disease and injury, identify people who are at risk, determine how to control or stop the spread or prevent it from happening again.⁵ They work to reduce risk and occurrence through research, community education and health policy.⁶

On a fundamental level, they’re looking for clues: who is sick, what their symptoms are, when they got sick, where they could have been exposed.

In the bigger picture, according to the Bureau of Labor Statistics (BLS), their tasks include these:⁶

• Plan and direct studies of public health problems to find ways to prevent and treat them if they arise
• Collect and analyze data—through observations, interviews, and surveys, and by using samples of blood or other bodily fluids—to find the causes of diseases or other health problems
• Communicate their findings to health practitioners, policymakers, and the public
• Manage public health programs by planning programs, monitoring their progress, analyzing data, and seeking ways to improve the programs in order to improve public health outcomes
• Supervise professional, technical and clerical personnel

Perhaps as a byproduct of pursuing these goals, epidemiologists have identified diseases that have never been seen before, such as Legionnaire’s disease, SARS and the organisms that cause them.⁵

In 2018, Nature Communications, the open-access journal offshoot of Nature magazine, published an editorial describing challenges to the definition of epidemiology as a science. The editors note that epidemiology “requires an understanding of how political, social and scientific factors intersect to exacerbate disease risk,”⁷ which makes it a unique science. Even so, criticisms include the idea that it is “simply a set of tools used by other disciplines, and that its dependence on observational data makes it a form of journalism rather than a science.”⁷

The editorial explains that this skepticism is due, among other causes, to epidemiology’s close relationship with so-called ‘soft sciences’—often thought of as less exact than other sciences owing to their focus on complex variables, such as human behavior and interactions, that are hard to quantify.

The editors oppose this view. “Socioeconomic and lifestyle factors, and features of the built environment, are known to affect health outcomes, including in individuals with cardiovascular and genetic diseases, and so they cannot be overlooked in studies of human health.”⁷

Epidemiological research, furthermore, has yielded dramatic results. “It is unquestionable that the discipline has saved millions of lives, from both infectious and non-communicable diseases, through interventions and preventative programs that have been implemented as a result of study findings. In fact, the CDC credits medical epidemiologists with adding 25 years to the average life expectancy of people living in the United States since 1947.”⁷

“Even more significantly … epidemiology continues to be at the forefront of saving lives today through forecasting epidemics and pandemics, and identifying diseases likely to cause outbreaks in the future and implementing forward-planning, targeted and collaborative interventions to minimize fatalities.”⁷

In concluding, the editors strongly endorse this “highly complex science” and invite submissions of articles from the field, “especially when applied to tackling issues of public health.”⁷

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