There was no doubt about the executives' IQs. They were all successful men who had demonstrated their ability to get ahead in highly competitive fields. But now their average age was 52, and many were older. Were they slipping? If so, how badly? In some cases, their employers wanted to know. In others, the men themselves wanted the answer. In all cases, Psychologists Willard A. Kerr of the Illinois Institute of Technology and Ward C. Halstead of the University of Chicago wanted to find out whether a man's mental ability necessarily declines with age.
Each executive took some tests that...