Dr. Ben Carson, being the first surgeon to successfully separate conjoined twins joined at the head, is arguably the best neurosurgeon in America, at least at his peak. Given there are about 3500 neurosurgeons in America, Dr. Carson’s job performance is +3.47 standard deviations (SDs) above his occupation’s mean on a normalized curve.

Given that IQ and job performance correlate about 0.6 in complex jobs (though this number may have been inflated by range restriction correction), then simple regression predicts Carson’s IQ is 0.6(3.47 SD) = 2.08 SD above the mean of neurosurgeons.

Assuming neurosurgeons are like other doctors, they probably average IQs around 125, with an SD around 11. Thus Carson’s expected IQ would be:

2.08(11) + 125 = 148

Of course these stats are based on typical neurosurgeons, and typical neurosurgeons, unlike Dr. Carson, are overwhelmingly non-black.

What happens when race is factored in?

For as long as IQ tests have existed, blacks Americans have scored about 15 points lower than white Americans. One interesting fact is that (partly because of affirmative action) this same 15 point IQ gap exists even among high achievers. On page 374 of his book Coming Apart Charles Murray reported IQs for educated white and black Americans. Because Murray reported his IQ data using American norms, I converted to the preferred scale using white American norms:

Whites with a bachelors degree: IQ 111
Blacks with a bachelor degree: IQ 96

Whites with a masters degree: IQ 114
Blacks with a masters degree: IQ 99

Whites with a PhD or professional degree: IQ 123
Blacks with a PhD or professional degree: IQ 110

As can be seen, at each level of accomplishment, blacks score roughly 15 points lower than whites. Extrapolating this trend to the best neurosurgeon in America (expected IQ of 148), would have an expected IQ of 148 – 15 = 133 if he’s black.

However, Dr. Carson is not just black, he’s a black Republican, and these probably average IQs about seven points lower than the average African American so we might, very crudely, subtract another seven points from his estimated IQ, bringing him down to 126, which is still higher than about 96% of white Americans.

Keep in mind, this is just a rough estimate, with a large margin of error. I’m aware of no actual data on Dr. Carson’s IQ.

I suspect Dr. Carson has a lopsided IQ. His verbal IQ is probably only around 100 judging from his slow speech and lack of general knowledge, but his spatial IQ is probably in the brilliant range, and on balance, he’s probably about 126, very roughly speaking.

This is unusual for blacks, who typically have a higher verbal than spatial IQ, probably because blacks had less exposure to the ice age, and thus less need to evolve the spatial ability to build fires, create tools, construct shelters, and sew clothes. It’s unclear why the good doctor seemingly has such a unique cognitive profile, but commenter JS suspects, based on his appearance, that he may have some East Asian ancestry.