Montaigne on Selection Bias

Another source of mistakes in belief formation is selection bias. Patients in dialysis centers are often surprisingly reluctant to be on the waiting list for a kidney transplantation. One reason is that all the transplanted patients they ever see are those for whom the operation failed so that they had to go back on dialysis. Montaigne was citing a bias of this kind when he referred to Diagoras as being “shown many vows and votive portraits from those who have survived shipwrecks and… then asked, ‘You, there, who think that the gods are indifferent to human affairs, what have you to say about so many men saved by their grace?’ — ‘It is like this,’ he replied, ‘there are no portraits here of those who stayed and drowned — and they are more numerous!'” Similarly, a psychiatrist who claims that “no child abusers ever stop on their own” neglects the fact that if any does he is unlikely to have met them. (Jon Elster, Explaining Social Behavior)