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death rate from the Southwark and Vauxhall Water Companies was about 9 times the death

rate for the Lambeth Water Compan

y 7 .

Snow’s publication of his results ‘On the Mode of Communication of Cholera’ by no

means unnerved advocates of the miasma theory. In their view the water of the mighty River

Thames would dilute all possible poisons to the point of ineffectiveness. Today, it is still not

uncommon to reject statistical argumentation as happened in Snow’s case: that is, that the

evidence provided did not prove that the water was contaminated.

The Broad Street Pump investigation

In epidemiological circles nowadays it is commonly agreed that one result achieved by

an investigation should also be validated by other investigations. Actually, that was done by

Dr. Snow in his extensive investigations into, what is now so famously remembered as the

‘Broad Street Pump’ investigation. In fact, the cholera outbreak in late August 1853 occurred

just in the neighbourhood of Snow’s living quarters. Snow reacted immediately by visiting the

area and found that quite a

number of the diseased had

already died. He discovered that

most fatalities had been living

around the Broad Street public

pump. He drew water from the

pump and, in comparison with

water from five other nearby

pumps, he found no difference in

the appearance of the water from

all the pumps. A microscopic test

of the water revealed many

organic materials, but this was

inconclusive. However, by then

he had embarked on what could

now be termed as the ‘mother of observational evidence’ in drawing a map of the area

indicating the location of the different public pumps and the houses of the 83 cholera deaths,

which he obtained from the General Register Office. In assessing the distance of the houses to

the nearest pump, it became obvious that 73 of the 83 cholera deaths were of people living in

homes for which the Broad Street pump was the nearest water source. The remaining 10

unfortunate victims were not living close to the Broad Street pump, but preferred the water

from that pump, or were children drinking its water on their way to school.

7 http://www.nada.kth.se/kurser/kth/2d5342/kurspaket/521.pdf

(retrieved 25.05.2015 From

Association to Causation: Some Remarks on the History of Statistic. By avid Freedman, Statistics

Department University of California, Berkeley, CA 94720, USA. Technical Report No. 521, 2002. Also

source of Table 1.