Beware Survivorship Bias
By Robert Higgs • Sunday April 3, 2016 2:18 PM PDT • 0 Comments
91 0 2
Suppose you wanted to know how many of the soldiers, sailors, and airmen who served during World War II were killed in that war. So you sent inquiries to a random sample of persons whose names were drawn from a list of all those who served in the military during the war, asking: Were you killed in the war? I presume that all of those who responded to the survey would reply, no. Having conducted your scientific poll, you could then conclude that none of the soldiers who served in the military services during World War II were killed.
The mistake you would have made in this case springs from what is known as survivorship bias. It affects many sorts of studies, including many where the study design is not so obviously stupid as in my foregoing example. Surveys have sought, for example, to determine how an increase in the legal minimum wage affected employers’ total hours of labor services hired. Such a forced wage-rate increase, however, especially if it were a large one, might well cause some marginal firms to go out of business. They would then be unavailable to respond to a poll or to show up in another type of survey to indicate that the increased minimum wage had caused them to reduce their hours of employment to zero, wiping out however many jobs they had previously supported.
Nenhum comentário:
Postar um comentário