Simpson’s Paradox

Here is a table that I used in my sample lecture to illustrate Simpson’s Paradox (in this case, two hospitals arguing about which one is better at curing patients).

(Well, in my original table there are borders between the columns too, but I haven’t worked out how to do that in WordPress yet! Hopefully the columns are clear enough anyway?)

In the following table, percentages have been rounded to the nearest integer


Male patients Female patients All patients
Hospital A 1 patient

1 cured

100% cured

9 patients

5 cured

56% cured

10 patients

6 cured

60% cured

Hospital B 90 patients

89 cured

99% cured

10 patients

3 cured

30% cured

100 patients

92 cured

92% cured


For more on this phenomenon, look up Simpson’s Paradox.

Situations like this really do turn up surprisingly often!


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