Re-Evaluating John Snow's 1856 South London Study

Social Science & Medicine

22 Pages Posted: 6 Aug 2020 Last revised: 4 Feb 2024

See all articles by Thomas Coleman

Thomas Coleman

University of Chicago - Harris School of Public Policy

Date Written: November 22, 2023


John Snow, the London doctor who studied cholera in the 1840s and 1850s, argued in Snow (1856) that water exerted an “overwhelming influence” on mortality in a region of south London during the 1854 outbreak. In a paper re-assessing Snow’s analysis, Koch and Denike (2006) claim that “Snow made not merely minor arithmetic errors but more importantly critical, conceptual mistakes that adversely affected his results.” The claim of errors and mistakes is incorrect and due to a misreading or misunderstanding of Snow’s data and analysis. Koch and Denike apply an inappropriate statistical test to Snow’s original data (and do so incorrectly). More importantly, due to the misreading of the historical record they alter the underlying primary-source data, rendering their results invalid. Analysis of the data following Snow’s approach but with modern statistical tools strongly supports Snow’s claim for the primacy of water in accounting for variation in cholera mortality.

Keywords: John Snow, Cholera, Causal Inference, Epidemiology, Statistical Methodology, History of Science

JEL Classification: C18, N33, N93, B40, C52

Suggested Citation

Coleman, Thomas, Re-Evaluating John Snow's 1856 South London Study (November 22, 2023). Social Science & Medicine, Available at SSRN: or

Thomas Coleman (Contact Author)

University of Chicago - Harris School of Public Policy ( email )

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