History of epidemiology

Concept

A few historical studies invented the methods used today: counting, mapping, comparing groups and following cohorts.

Updated Nov 13, 2026

Key points

John Graunt (1662) analysed London's death records and was the first to quantify patterns of birth, death and disease.
William Farr, in the 19th century, organised Britain's mortality statistics: he is considered the father of modern vital statistics and surveillance.
John Snow (1854) mapped cholera deaths around the Broad Street pump and compared rates by the company supplying the water: a map and a natural experiment.
Edward Jenner (1796) inoculated a boy with cowpox material and showed protection against smallpox: the origin of vaccination.
Ignaz Semmelweis (1847) required handwashing with chloride of lime in the clinic staffed by doctors and students, and maternal deaths fell.
Framingham (since 1948) is a prospective cohort on cardiovascular disease; Doll and Hill linked smoking to lung cancer with a case-control study (1950) and then a cohort of doctors.

What it is

Epidemiology grew out of counting deaths and births and comparing groups to find causes before mechanisms were known. Each historical milestone teaches a method: counting deaths, mapping cases, the natural experiment, comparing services, the prospective cohort and the case-control study. Knowing them helps to remember what each design is for.

Worked example

Made-up scenario in the style of Semmelweis: two delivery wards take mothers on alternate days.
Ward A (doctors): 900 births and 27 deaths from puerperal infection: 27 / 900 = 30 per 1 000.
Ward B (midwives): 900 births and 9 deaths: 9 / 900 = 10 per 1 000; rate ratio 30 / 10 = 3.
Handwashing is introduced in ward A only; the next year it has 1 000 births and 11 deaths: 11 per 1 000.
Reduction in ward A: (30 − 11) / 30 = 19 / 30 ≈ 63 %; ward B stays at 10 per 1 000.
New rate ratio: 11 / 10 = 1.1; the gap between the wards almost disappears.
Reading: ward B, which did not change, acts as a concurrent control and shows the fall was not just the passage of time.

The method each milestone teaches

Milestone	Year	Method	Lesson
Graunt, London records	1662	Counting vital statistics	Counting well already reveals patterns
Jenner, cowpox	1796	Exposure-and-challenge experiment	An intervention can be tested; today it would be ethically unacceptable
Semmelweis, Vienna clinics	1847	Group comparison and before-after intervention	A cause can be controlled before the agent is known
Snow, cholera in London	1854	Spot map and natural experiment	Comparing exposure sources without assigning them
Doll and Hill, smoking	1950 and 1951	Case-control, then cohort	Two designs reaching the same answer strengthen causation
Framingham	1948	Prospective population cohort	Identifying risk factors for chronic disease

Markers

Graunt
Farr
Snow
Jenner
Semmelweis
Framingham
Doll and Hill

In practice

Snow's logic is used in every outbreak today: map the cases, form a hypothesis about the source, compare exposed and unexposed people.
Semmelweis is a reminder that evidence is not enough: his measure was resisted in his time; implementation is part of public health.
Smallpox eradication (last natural case in 1977; declared in 1980) showed how far vaccination can go.

Common pitfalls

Telling history as hero stories and forgetting the method: what is examined is which design each case illustrates.
Believing Snow knew the cholera bacterium: he acted on distribution data without knowing the agent.
Mistaking the Framingham cohort for a trial: nobody assigned the risk factors; they were observed.

Test yourself

Think of the answer, then tap the question to see it.

Which two methods does John Snow's work on cholera in London illustrate?

The spot map of cases around a water pump and the natural experiment comparing rates by the company that supplied each house's water.

What did Semmelweis do in 1847, and what does it teach about method?

He required handwashing with chloride of lime in the clinic of doctors and students; maternal deaths fell. It shows that comparing groups lets a cause be controlled without knowing the agent.

Which design did Doll and Hill use first to study smoking and lung cancer, and which later?

First a case-control study (published in 1950), then a prospective cohort of British doctors started in 1951.

Why is the Framingham study a milestone?

It is a prospective population cohort begun in 1948 that identified cardiovascular risk factors such as high blood pressure, high cholesterol and smoking.

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Connections

← All of epidemiology

Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.

Sources: Principles of Epidemiology | Lesson 1 - Section 2 (Centers for Disease Control and Prevention, 2012); History of Smallpox (Centers for Disease Control and Prevention, 2026); Ignaz Phillip Semmelweis’ studies of death in childbirth (The James Lind Library, 2026); Framingham Heart Study (FHS) (National Heart, Lung, and Blood Institute (NHLBI), NIH, 2026).

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Representative model, for educational purposes only.