In honor of President’s Day, I am going to do a few posts today about U.S. presidents, but because it’s also Family Day (here in Ontario), I will start by discussing the Bush family (a family of Presidents, thus combining Family Day and President’s Day!).

A reader asked me to estimate the IQ of George H.W. Bush and this is fairly easy, because we know from SAT scores that his son (George W. Bush) has an IQ equivalent of about 125 (U.S. norms).

The IQ correlation between one parent and one child is 0.45, so if all we knew about George H.W. Bush was that his son has an IQ of 125, our best guess for George H.W. Bush’s IQ would be 45% as far from the U.S average as his son:

Expected IQ = 0.45(25) + 100

Expected IQ = 111

However we also know that George H.W. Bush is a U.S. president, thus when guessing his IQ, we should regress the expected IQ, not to the average of all Americans, but to the average of American presidents, which appears to be about 130.

The average U.S. president would likely have an offspring with an IQ of 30(0.45) + 100 = 114, so George H.W. Bush has a son that is 11 points above the average of presidential kids. Thus George H. W. Bush would have an expected IQ of:

Expected IQ = 0.45(11) + 130

Expected IQ = 135

So my guess is that George H.W. Bush was about 10 IQ points smarter than George W. Bush.  This may help explain why the father had the good sense not to topple Saddam Hussein, but the son didn’t.

However his son is 11 points smarter than the average President’s offspring.  This may help explain why the son was smart enough to become President just like his Dad, something the vast majority Presidents’ kids never come close to achieving.

Now, some might object that in a restricted sample like U.S. presidents, the parent-child correlation would be lower than 0.45, however since that correlation was likely derived from testing offspring when they are very young, and since George W. Bush was tested near adulthood, it’s probably an underestimate anyway, so reducing it in a restricted population would be redundant.

Of course, this is just a rough statistical prediction, and should not be considered a substitute for actual test scores.