Steve Rubenzer, in the Boston Globe (June 13, 2004):

Harry Truman said that being dumb was just about the worst thing for a president. Was he right? Or are there other personality traits that can predict the success of the occupant of the White House?

We recently examined the personalities of all 43 presidents; we asked 120 authors of presidential biographies to complete personality assessments of the men they studied. These ratings were correlated with assessments of presidential greatness by historians. Using our data, University of Minnesota professor Deniz Ones, an expert on the relationship of personality to job performance, identified nine personal qualities that can be counted on to determine presidential success.

* Rated intelligence. We asked our raters how bright they perceived the various presidents to be. Those who received high ratings, like Thomas Jefferson, Teddy Roosevelt, and Woodrow Wilson performed better than those rated as less gifted, like Warren G. Harding. There are exceptions: Andrew Jackson was the greatest president of his age, yet he ranked low on intellectual giftedness. So, ironically, did Harry Truman, who was rated in the lower third.

* Assertiveness, or the capacity to influence through one's presence and ideas, is the most important indicator of presidential success. Presidents are an assertive group, and on average, they score higher than eight of 10 typical Americans. Better presidents like the Roosevelts, Wilson, and Jackson score higher than average chief executives. Truman is the only successful president who was less assertive than his peers. Low scorers include Warren G. Harding, William Howard Taft, and Calvin Coolidge.

* Positive emotions. A president's optimism and enthusiasm are important indicators for job performance. They're also important for getting elected. High spirited presidents like the Roosevelts, Bill Clinton, and John F. Kennedy are typically more successful. The more reserved presidents, like John Quincy Adams, Herbert Hoover, and Richard Nixon, had less successful presidencies. But here, again, there are exceptions: George Washington was the only truly successful chief executive who scored low on this scale.....

For the most part, the same traits that make good presidents also tend to make successful CEOs, but there are two exceptions. Low straightforwardness has not been identified as a desirable quality in business leaders, nor has tender-mindedness. It may be that the job of president differs from other executive roles because of the diversity of the constituency and the scale of the stage.