2. Epidemiology Basics

• Pages: 21-49
• Author: Chester C. Clarke,Mark A. Roberts

2

Epidemiology Basics

Chester C. Clarke, MD, MPH, and

Mark A. Roberts, MD, PhD, FACOEM1

In disease outbreak litigation, epidemiological studies typically play

an essential role in proving—or disputing—causation. This chapter

provides a basic orientation and tools to help litigators understand

and evaluate epidemiological evidence. The chapter includes a brief

history of how the eld of epidemiology has evolved, denitions of

key terms, a description of various types of epidemiological stud-

ies with their strengths and weaknesses, and a discussion of nine

widely accepted criteria for assessing apparent causal relationships.

The COVID- 19 pandemic of 2020 brought epidemiology, both

descriptive and analytic, directly into focus for both the medi-

cal and scientic communities, as well as the general public. Every

day on the news, one would hear about the number of cases with

a description of their gender, age, etc. The news media introduced

many to the intricacies of epidemiology and to the complicated pro-

cess of scientic discovery. Daily news coverage highlighted the dif-

culties of moving from association to causation and from empiric

1. Chester Clarke is a Managing Scientist in Health Sciences at Exponent, Inc. Mark

Roberts is a Principal Scientist in Health Sciences at Exponent, Inc.

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treatment to studies of clinical efcacy. The efcacy of treatments

such as hydroxychloroquine were debated in the media as physician

researchers and public health ofcials reminded us about the need

for clinical trials—that is, analytic epidemiology—to be able to know

whether a treatment was truly effective or not.

But rst, what is epidemiology? As the late Professor Leon Gordis

noted in his classic text on the subject, “Epidemiology is the study of

how disease is distributed in populations and of the factors that inu-

ence or determine that distribution.”2 Professor Robert Wallace calls

it “the basic science and most fundamental practice of public health

and preventive medicine.”3 Looking at populations, the epidemiol-

ogist is able to see trends about disease that the clinician who sees

the individual patient cannot see. This wider perspective enables the

epidemiologist to describe certain attributes of the disease, such as

incubation period, transmission, demographics of patients with the

disease, patterns of disease, etc.—which then help the clinician with

diagnosis, treatment, and possibly prevention of additional cases.

For example, a clinician sees a patient with red hair who has disease

A. The clinician then sees several other patients who have disease A

and red hair, and begins to think that there is a relationship (asso-

ciation) between disease A and red hair. The epidemiologist studies

many more people who have disease A. By comparing the proportion

of people who have disease A and red hair to the proportion of people

who do not have disease A but who have red hair, the epidemiologist

can discern whether or not there is a true relationship between disease

A and red hair.

Epidemiology has many varied applications. For example, epide-

miology is the basis for clinical trials used in the evaluation of new

drugs in addition to investigations of post- marketing issues. Epidemi-

ology plays a part in the surveillance of populations to alert the pub-

lic health community to an outbreak, such as what happened recently

in the case of measles in New York State. Epidemiology is used in

the analysis of disease transmission; disease progression; the reliabil-

ity and validity of tests for both diagnostic and screening purposes;

2. Gordis L. Epidemiology. W.B. Saunders Company; 1996:3.

3. Wallace RB. Epidemiology and public health. In: Wallace RB, ed. Maxcy- Rosenau-

Last Public Health & Preventive Medicine. 15th ed. McGraw Hill Medical; 2008.

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