By Bryan Caplan
One lovable thing about Weeden and Kurzban’s The Hidden Agenda of the Political Mind: When they criticize me, they also quietly hand readers my rebuttal. Them:
Economist Bryan Caplan in his book, The Myth of the Rational Voter, asserted (with his tongue in its usual non-cheeky place): “There are countless issues that people care about, from gun control and abortion to government spending and the environment… If you know a person’s position on one, you can predict his view on the rest to a surprising degree. In formal statistical terms, political opinions look one-dimensional. They boil down to roughly one big opinion, plus noise.”
If we take the assertions from Caplan and Pinker (not to mention Stewart) seriously, we should be able to take people’s view on one of these issues and know their views on the other issue…
The data are decidedly less tidy.
Just one problem: I’m well-aware that the data aren’t tidy. Accurately predicting individual opinions is hard. I deliberately included the words “plus noise” to ensure that readers knew I was not claiming great predictive powers.
I should add, however, that opinion has more ideological coherence than Weeden and Kurzban claim. Yes, using one specific issue position to predict an unrelated specific issue position is almost fruitless. In the General Social Survey, the correlation between gun control and abortion positions is a mere .02. But using self-identified ideology to predict specific issue positions is noticeably more rewarding. In the GSS, ideology correlates at .11 with gun control views and .22 with abortion views.
Why would this be? Simple. Specific issue views, like individual items on the SAT, are very noisy. Ideology, like overall SAT score, is not so noisy. When you correlate two noisy things with each other, you get a really tiny correlation. When you correlate one noisy thing with a not-so-noisy thing, you get a moderate correlation. If Weeden and Kurzban really wanted to dispute the one-dimensionality of political opinion, they should have been correlating specific issue views with ideology, not specific issue views with each other.