We're getting a new Prez tomorrow: let's look at the issue of IQ again. I looked at a research article by Dean Simonton ("Presidential IQ, Openness, Intellectual Brilliance, and Leadership," Political Psychology, 27, 4, 2006). He seems to do a pretty careful job. He uses multiple ratings by multiple experts with multiple methods to estimate the IQs and the leadership performance of 42 Presidents.
So, what is the correlation between IQ and greatness? It ranges between .31 and .35, depending on the measure of IQ. If we average the correlations, R-squared is .11, which means that IQ tells 11% of the story. (This is fairly close to Charles Murray's estimate of 16%).
On the one hand, cognitive ability is not a trivial matter. As Steve Sailer wrote, IQ is probably more important than any of the other factors you can identify. On the other hand, 11% is not impressive up against everything else--the other 89%. Plus, the 11% would probably be lower in a multivariate analysis.
You might respond that this doesn't make sense because it is simply impossible that someone with, say, a 95 IQ could perform well at such a demanding job. But that is not what the results imply. They are saying that within the range of IQs that we've seen among presidents, differences in IQ are not that critical. From the lowest estimate of 107.8 (Harding) to the highest of 175.0 (J.Q. Adams), the range is high enough for other factors to become important. (By the way, the high estimate for Harding is 139.9).
Quoting Sailer again, quoting Greg Cochran, "What really matters in a leader is not being smart, but being right. Who was smarter? Warren G. Harding or V.I. Lenin? I'm sure Lenin could have beaten Harding in chess, but I definitely would rather have lived under Harding than Lenin. Harding was kind of a dumb bunny, but his prejudices and instincts were much more reasonable than Lenin's, who was wrong about everything."
In my judgment, Obama is smart as hell. So what. He's wrong.
While we're at it, the study puts G.W. Bush's IQ somewhere between 111 and 138.5, with a mean of 125. This is close to the 125-130 range given by Sailer.
Also--see any numbers that seem way off in the table? Why is Coolidge about the same as W. and Harding?