Snow and cholera
Problem
On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated decidedly nearer to another street-pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street, as they preferred the water to that of the pumps which were nearer. In three other cases, the deceased were children who went to school near the pump in Broad Street...
With regard to the deaths occurring in the locality belonging to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the pump water from Broad Street, either constantly or occasionally...
The result of the inquiry, then, is, that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump well.
I had an interview with the Board of Guardians of St James's parish, on the evening of the 7th inst [Sept 7], and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.
- What is Cholera ?
- From the text above [or from your own research using internet resources - see Hint for a starter link] pick out information which supports the parish Board of Guardian's decision to make the Broad Street pump unusable by removing the pump handle.
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Was the decision certain to be correct ?
Getting Started
The circumstances surrounding the story of John Snow and the Broad Street pump are explained on this website supported by the Science Museum. Making the Modern World
Putting 'Snow Broad Street Pump ' into Google will bring up even more information.
And this article gives more background on Understanding Hypotheses .
Student Solutions
Thanks to Patrick from Woodbridge School for his thoughts responding to this problem.
Look at the Hint page for more links to information.
Here's what he says : Cholera is a bacterial disease that often kills, usually by dehydration or lack of vital salts. It causes extreme diarrhoea and vomiting, and the water loss from the dehydration causes the blood to turn black and the skin blue.
The main supporting evidence for the decision is:
... found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated... nearer to another street-pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street... In... other cases, the deceased were children who went to school near the pump in Broad Street...
... [There] were 61 instances in which... the deceased persons used to drink the pump water from Broad Street...
The result of the inquiry, then, is, that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump well. This is strong evidence, but the evidence cannot confirm with absolute certainty that this is the cause - there could have been another cause unrelated to the pump, in which case the decision would have been incorrect.
Thanks Patrick
Teachers' Resources
Why do this problem :
This problem calls for good application of practical reasoning and is a great simple example of the process of making and testing hypotheses.
Possible approach :
Start by discussing epidemics, or Cholera in particular, using the supporting material. The main task is for students to think about what information, recorded in the text, allowed John Snow to recommend a course of action. Explain that John Snow was a pioneer in medicine in London in the 19th century who thought that diseases such as Cholera were water-borne. As news of this outbreak reached him he went quickly to the Broad Street area of London before too many people had fled so that he could ask questions that would help him form a view about the likely cause of the disease. A key concept to draw out as students discuss the task and the context is that a hypothesis is never completely settled. It is more useful to describe it as a process of increased confidence in our account of the situation.
Key question :
-
What is Cholera ?
-
Which information supports the parish Board of Guardian's decision to make the Broad Street pump unusable by removing the pump handle ?
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Was the decision certain to be correct ?
Possible support :
The problem In the Bag takes students to the heart of hypothesis-making in a very simple way : samples, even a large number of samples, never settle the question beyond all doubt, they do however increase confidence in our belief. It ceases to be a hypothesis when we open the bag and reveal the actual contents.
And this article gives more background on Understanding Hypotheses.