Let’s assume Reagan had the lowest elderly IQ of any U.S. President (he got dementia) and Nixon had the highest teenaged IQ (he aced the Ottis). What does this tell us about the average IQ of U.S. Presidents?

Reagan

About one in six (British?) people over age 80 have dementia. Thus one can consider a dementia diagnosis (over age 80) as more or less equivalent with scoring at or below the 16th percentile (IQ 85) on an IQ test. On the other hand, only the best and brightest tend to live over 80. If everyone in the UK lived over 80, probably 25% would get dementia and the 25th percentile equates to IQ 90.

Nixon

Daniel Seligman wrote:


 Nixon biographer Roger Morris says RMN tested at 143 when he was in Fullerton High School in California. Kennedy biographer Thomas C. Reeves tells us JFK tested at 119 just before entering Choate Academy. That last figure looks low. Might there have been some kind of testing error? The ”standard error” for the Otis test — the one taken by both future Presidents — was six IQ points.

Fortune magazine, July 15, 1991

I had since learned that the Otis had a standard deviation of about 10 in those days so Nixon’s IQ of 143 would actually equate to about 165 on the standard 15 sigma scale, making him almost certainly the smartest U.S. President ever. Of course the Otis items were not selected at random, so there’s no reason to assume the curve was Gaussian, and thus equivalent to a modern IQ of 165. On the other hand there’s no strong reason to assume it was less than that either.

Conclusion

Assuming Reagan had an IQ around 90 (probably higher when he was younger) and Nixon had an IQ of 165 (probably lower when he was older), let’s split the difference and assume the average U.S. President has an IQ around 130 (two standard deviations above the U.S. mean).

Just as the most physically dominant men in America (heavy weight boxing champions) are 2 standard deviations taller than the average U.S. man (on average), the most socially dominant men in America (U.S. Presidents) are about 2 standard deviations smarter.