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sionnach commented on the word simpson's paradox
Suppose we want to compare two treatments, A and B, for a particular disease. 160 patients are given A - 60 recover; 230 patients receive B and 65 recover.
Clearly, treatment A, with a cure rate of 60/160 = 38%, is preferable to treatment B, with cure rate 65/230 = 28%. Right?
Maybe not. What if we are also given the recovery rates by sex, as follows:
men : A 20/100 (20%) B 50/210 (24%)
women: A 40/60 (67%) B 15/20 (75%)
overall: A 60/160 (38%) B 65/230 (28%)
Thus, even though A appears better overall, clearly treatment B is better both for men and for women. This contradiction is known as Simpson's paradox.
October 16, 2007