The source: “Presidential IQ, Openness, Intellectual Brilliance, and Leadership: Estimates and Correlations for 42 U.S. Chief Executives” by Dean Keith Simonton, in Political Psychology, August 2006.

Anybody who has ever been to an American high school knows that intelligence doesn’t always equal success either in the adolescent world or in life. A new study of the intelligence quotients (IQs) of the 42 U.S. presidents is similarly confounding. Our smartest president, John Quincy Adams, was defeated after only one term and spent the rest of his life in the House of Represen­tatives. Our dullest, Ulysses S. Grant, according to the study, won the Civil ­War.

Dean Keith Simonton, a psychologist at the University of California, Davis, estimated the IQs of the presidents based on their writings, early developmental milestones, openness to ideas, and other traits generally associated with intelligence. Simonton also drew on previous studies by other researchers. Biographical profiles of each president, stripped of identifying factors, were prepared, and traits such as ‘‘inventive,” ‘‘curious,’’ and “sophisticated” were assessed. Missing values were imputed using standard statistical tech­niques. All the presidents scored at least 130, in the top 2.2 percent of the population. The average IQ is ­100.

Simonton found that John Quincy Adams, son of President John Adams and the nation’s sixth president, had an estimated IQ
of 175. Other top scorers were Thom­as Jefferson, 160; James Madison, 160; John F. Ken­nedy, 159.8; and Bill Clinton, 159. The lowest, Grant, scored 130 on a measure­ment of his IQ. Next lowest was President George W. Bush, at ­138.5.

Simonton writes that although George W. Bush’s estimated IQ is below average when compared to those of other chief executives, he is “certainly smart enough to be president of the United States.” Bush’s scores were dragged down by his lack of “openness”—to aesthetics, feelings, actions, ideas, and ­values—­and something called “integrative complexity,” a gauge of the ability to integrate multiple perspectives on an issue into a coherent point of ­view.

Simonton acknowledges that intellect is not by any means the only predictor of good presidential leadership, but says that, “the conclusion remains, however tentative at this point in time, that Bush’s intellect may be more a liability than an asset. . . .  His strengths most likely lie elsewhere.”