The single strongest predictor of a person’s IQ is the IQ of his or her mother.
However, once you get beyond the school environment, it’s not a very reliable predictor of performance. Controlling for other factors, people with high IQs do not have better relationships and better marriages. They are not better at raising their children. In a chapter of Handbook of Intelligence, Richard K. Wagner of Florida State University surveys the research on IQ and job performance and concludes, “IQ predicts only about 4 percent of variance in job performance.” In another chapter of the handbook, John D. Mayer, Peter Salovey, and David Caruso conclude that at best IQ contributes about 20 percent to life success.
One famous longitudinal study known as the Terman study followed a group of extremely high-IQ students (they all scored 135 or above). The researchers expected these brilliant young people to go on to have illustrious careers. They did fine, becoming lawyers and corporate executives, for the most part. But there were no superstar achievers in the group, no Pulitzer Prize winners or MacArthur Award winners. In a follow-up study by Melita Oden in 1968, the people in the group who seemed to be doing best had only slightly higher IQs. What they had was superior work ethics. They were the ones who had shown more ambition as children.
A global survey by Adrian Furnham of University College, London, found that men everywhere overestimate their own intelligence. Another study revealed that 95 percent of American men believe they are in the top 50 percent when it comes to social skills. Women are more likely to be status deflaters. Women underestimate their IQ scores by an average of about five points.
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