The reverential status of randomized, controlled trials in medicine is its own source of bias. The BCG vaccine against tuberculosis was shown to have a potent protective effect in a randomized trial, but the effectiveness of the vaccine seems to decrease almost linearly as we move in latitude from the North to the South—where, incidentally, TB is the most prevalent (we still don’t understand the basis for this effect, although genetic variation is the most obvious culprit). These distortions—call them heuristic biases—are not peripheral to the practice of medicine. Virtually every day I’m asked to decide whether a particular drug will work for a patient—an African-American man, say—when the trial was run on a population of predominantly white men in Kansas. Women are notoriously underrepresented in randomized studies.

The reverential status of randomized, controlled trials in medicine is its own source of bias. The BCG
vaccine against tuberculosis was shown to have a potent protective effect in a randomized trial, but the
effectiveness of the vaccine seems to decrease almost linearly as we move in latitude from the North to the
South—where, incidentally, TB is the most prevalent (we still don’t understand the basis for this effect,
although genetic variation is the most obvious culprit). These distortions—call them heuristic biases—are
not peripheral to the practice of medicine. Virtually every day I’m asked to decide whether a particular
drug will work for a patient—an African-American man, say—when the trial was run on a population of
predominantly white men in Kansas. Women are notoriously underrepresented in randomized studies.