Data Viz 101: Florence Nightingale, John Snow, and Prescriptive Visualizations

Welcome back to Data Viz 101, Beutler Ink's introductory seminar on the wonderful world of data visualization.

In the last installment, we looked at the pioneering work of William Playfair, a Scottish engineer and political economist often credited as the inventor of statistical graphics. For this post, we'll look at the contributions of Florence Nightingale and John Snow, who both used data visualizations to advance prescriptive public health solutions.

In 1857, Florence Nightingale (1820–1910), the "lady with the lamp" and mother of modern nursing, returned to Britain from the front lines of the bloody (and boozy) Crimean War with a circular histogram, or "rose diagram," to illustrate the seasonal sources of soldiers' fatalities.

Her diagram depicted twelve spokes, one for each month of the year. Each spoke was split into color-coded wedges which represented different causes of death. The blue wedges—clearly the largest—represented deaths from infectious but preventable diseases. The much smaller red wedges represented death from wounds, while the tiny black wedges death from "all other causes."  

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The diagram provided a compelling and immediately understandable illustration of a startling statistic: out of the 18,000 soldiers who had died, 16,000 had died of disease in hospital, rather than their wounds. Nightingale made extensive use of such diagrams in presenting reports on medical care throughout the war, and was able to persuade Queen Victoria and Members of Parliament to improve conditions in military hospitals.

If Nightingale was the mother of modern nursing, then John Snow (1813–1858) was the father modern epidemiology, in part due to his work in tracing the source of a 1854 cholera outbreak in the Soho district of London. The prevailing belief at the time was that cholera and other diseases were transmitted by "bad air." But by collecting the locations of cholera deaths, Snow was able to identify a clear concentration around the water pump on Broad Street. His research was persuasive enough to persuade the local city council to disable the well pump by removing its handle. This action has been commonly credited as ending the outbreak.

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Snow later used a map to illustrate the cluster of cholera cases (shown as bars parallel to the street at the appropriate addresses) around the pump. This early form of a dot map, along with Snow's other work on the case, helped change how scientists understood the cause and spread of disease.

This post from UC Berkley's Ani Adhikari and John DeNero has a more detailed analysis of John Snow's map and subsequent investigations. And heads up: Next week, we'll shift from history to form with a deep look at line graphs.

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