← Detective's Desk
0/6 sections complete done☰ All chapters
The Shoe-Leather Files/Chapter 3
03

What Epidemiologists Actually Do

The roles of epidemiology in public health, and the steps to solving a health problem

Since the 1980s, public health has recognized six core jobs that make up the work of epidemiology. A single epidemiologist might do all six over the course of a career, sometimes all six in the same investigation.

01
Surveillance

Continuously watching disease patterns so problems are caught early. (Section 6!)

02
Field Investigation

Going out (literally, "shoe leather") to find cases and clues during an outbreak.

03
Analytic Studies

Running rigorous studies (like case-control or cohort studies) to test a hypothesis.

04
Evaluation

Checking whether a program or intervention is actually working as intended.

05
Linkages

Teaming up with labs, doctors, and other agencies: field epi is a team sport.

06
Policy Development

Turning evidence into recommendations, regulations, and guidelines.

No matter which of these six roles they're playing, every epidemiologist follows the same basic logic when solving a health problem, sometimes called the epidemiologic approach:

#
Count

Find and count the cases or health events, describing them by time, place, and person.

÷
Divide

Divide the number of cases by the size of the population at risk to calculate a rate.

⇄
Compare

Compare that rate over time, or against another group, to see if it's really unusual.

Step zero: define a "case." Before anyone can count anything, epidemiologists agree on a case definition, the exact clinical and lab criteria that decide whether a person counts as a case. A shared case definition means a health department in 2024 can compare its numbers fairly against 2019, or against another state entirely.

✓ Check Yourself

Tap each question to check your answer · 0 of 1 opened

Q4What are the three basic actions every epidemiologist takes with data, in order?
Count cases (by time, place, person), divide by the population at risk to get a rate, then compare that rate across time or groups.