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# 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.

## Memory aid

‘Count, map, compare, follow’: Graunt counted, Snow mapped, Semmelweis compared and Framingham followed people for decades.

## 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

## Related 6

- [What epidemiology is](https://durgical.com/en/epidemiology/what-epidemiology-is/)
- [Outbreak investigation](https://durgical.com/en/epidemiology/outbreak-investigation/)
- [Cohort study](https://durgical.com/en/epidemiology/cohort-study/)
- [Case-control study](https://durgical.com/en/epidemiology/case-control-study/)
- [Bradford Hill criteria for causation](https://durgical.com/en/epidemiology/bradford-hill-criteria-for-causation/)
- [Public health surveillance](https://durgical.com/en/epidemiology/public-health-surveillance/)

## Related conditions 2

- [Cholera](https://durgical.com/en/conditions/cholera/)
- [Lung cancer](https://durgical.com/en/conditions/lung-cancer/)

[← All of epidemiology](https://durgical.com/en/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](https://archive.cdc.gov/www_cdc_gov/csels/dsepd/ss1978/lesson1/section2.html) (Centers for Disease Control and Prevention, 2012); [History of Smallpox](https://www.cdc.gov/smallpox/about/history.html) (Centers for Disease Control and Prevention, 2026); [Ignaz Phillip Semmelweis’ studies of death in childbirth](https://www.jameslindlibrary.org/?p=1146) (The James Lind Library, 2026); [Framingham Heart Study (FHS)](https://www.nhlbi.nih.gov/science/framingham-heart-study-fhs) (National Heart, Lung, and Blood Institute (NHLBI), NIH, 2026).

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Representative model, for educational purposes only.

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