Category THE PATH FROM CAUSE TO EFFECT

Masters of ’Metrics: John Snow

British physician John Snow was one of the fathers of modern epidemiology, the study of how illness moves through a population. Studying an outbreak of cholera in London in 1849, Snow challenged the conventional wisdom that the disease is caused by bad air. He thought cholera might be caused by bad water instead, an idea he first laid out in his 1849 essay On the Mode of Communication of Cholera.

A further cholera outbreak in 1853 and 1854 claimed many lives in the London neighborhood of Soho. Snow attributed the Soho epidemic to water from a pump on Broad Street. Not afraid to give a natural experiment a helping hand, he convinced the local parish council to remove the handle of the Broad Street pump...

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