John Snow and data visualisation
© Unknown
John Snow
At the Clinical Research Network we are moving towards our own "AppCentre" that will facilitate new and exciting insights from our data. It seems a timely moment to reflect on the beginnings of data visualisation and business intelligence and to remember the famous, first "case study".

In the mid-19th century, the Soho district of London had a serious problem with filth due to the large influx of people and a lack of proper sanitary services: the London sewer system had not reached Soho. The London government decided to dump the waste into the River Thames and this action contaminated the water supply, leading to a cholera outbreak.

On 31 August 1854, a major outbreak of cholera struck Soho. Over the next three days 127 people on or near Broad Street died. In the next week, three quarters of the residents had fled the area. By 10 September, 500 people had died and the mortality rate was 12.8% in some parts of the district.

This outbreak is best known for the physician John Snow's study of it and his discovery that cholera is spread through contaminated water. John Snow was a sceptic of the then dominant miasma theory that stated that diseases such as cholera or the Black Death were caused by pollution.

By talking to local residents, Snow identified the source of the outbreak as the public water pump on Broad Street. Snow took his evidence in the form of data lists to the London government to ask them to remove the handle from the pump, thus closing it down and disrupting the link to the spread of the disease. The government of the time dismissed the lists, still wedded to the idea that the illness was spread through the air.

Snow, convinced he was correct, considered how to portray the data differently. He decided to use a spot map to illustrate how cases of cholera were centred on the pump. He also made a solid use of statistics to illustrate the connection between the quality of the source of water and cholera cases. Showing the connection between cholera and water sources visually convinced the politicians.

As we move towards our own "AppCentre", I thought it would be useful to reiterate how using data in new ways can enable us to answer important questions and further evolve how we look at problems.