Consider the following hypothetical experiment to examine whether taking a headache pill reduces a headache. The 40 participants in the treatment group took a pill for their headache, and 50% of them have been cured. The 40 participants in the control group did not take the pill, and only 40% them have been cured. The results are in the table below. It seems clear that the pill helps reduce headaches.
| | Headache Gone | Headache Not Gone | % Cured
|
| Pill | 20 | 20 | 50 |
| No Pill | 16 | 24 | 40 |
However, suppose that this experiment did not properly randomize the assignment of subjects to the treatment or control groups. How can a confounding variable (e.g., the gender of the test subjects) invalidate the outcome above?
2 comments:
Simpson's paradox?
Yes, it is indeed Simpson's paradox =)
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