Wednesday, December 11, 2013

The IQ Horseshoe

Part of the paper I'm writing with Alex Nowrasteh over at Cato has bits in it on opinions on specific policy issues. If you're reading this (and I have every reason to assume you are reading this), there's a pretty good chance that you're familiar with my fondness for Stata's MARGINSPLOT command. You may also be familiar with my fondness for ordered probit regressions using GSS data. It's a wonderland, people. Combine the two, and I'm like Jack Skellington in Sandy Claws gear, filled with dreadful Christmas cheer.

Take a look at these, would you?

What doth these? Margins, of course. Specifically, margins of this regression:

oprobit natcrime i.partyid i.immcat i.polviews i.female i.race i.age i.degree i.wordsum loginc, cluster(year)

Of the form

margins wordsum#female, predict(outcome(n))

where n $\in \!\,$ [1,2,3], obviously.

Basically what I've done is asked the GSS how folks feel about (in this case) federal spending on crime prevention and looked at the margins based on their IQ proxy, which is the ability to get vocabulary words right. I then, for reasons not entirely germane to this post in particular, wrung two separate series out of each margins command, divvied up by sex. Nothing especially fancy.

But the results are very curious, and they seem to more or less hold up across a multitude of these spending questions. At the low end, we see noise (indicated by the big error bars), which is what we expect of folks with low IQ: they have inconsistent, often irrational beliefs. No big news there. But the hell of it is in the point estimates. What's with the horseshoe? Someone who only gets 2 of 10 vocabulary words right is about as likely to think that the government spends too little on crime as someone who gets 9 of 10 words right. But someone who gets 5 right is about 7% more likely to hold the same opinion. Now, I haven't done pairwise significance testing, but the eyeball check shows point estimates outside rival error bars, so it's probably teasing the 95% threshold at least, but even without that, I find the shape of these curves compelling.

And I'm not entirely sure what to make of it. For the crime stuff anyway, we might imagine that low-IQ folks are of the "I don't trust the police" type and the high IQ folks are in the "violent crime has empirically decreased in the past century" camp, with the middling folks picking up the slack, but that's just a wild guess.

Anyway, I thought it was a cool little snippet of empirical evidence I thought would be fun to share. Enjoy the rest of your day, and drive safely.