Jonathan Adler recently blogged about a paper on the markedly higher productivity of conservative and libertarian law professors. Some people noted weaknesses in the paper, and argued against its validity. Here is what Phillips, the paper’s author, had to say:

The data I examine–individual-level professor qualifications, and annual publication and citation rates–allow for a better investigation of the last two hypotheses (Brainpower and Discrimination) compared to the first two hypotheses. The first two–Greed and Interest–are self-selection hypotheses. Conservatives and libertarians do not enter legal academia by their own choice, choosing to pursue more financially lucrative or personally rewarding career paths. The other two hypotheses are ones of barriers to entry, one legitimate (Brainpower) and one arguably not (Discrimination).

Comments have centered around three main points. First, the data are also consistent with one of the self-selection hypotheses. Second, conservatives/libertarians are more likely to get clerkships, undermining the findings some. Third, annual publication and citation rates aren’t good measures of law professor ability or success, and if they were, wouldn’t the market correct any discrimination? Let me address each in turn.

If the Greed Hypothesis is the sole explanation, then we could expect conservatives/libertarians to pursue careers where they could make the most money. Thus, the more capable would not enter legal academia since they could make more money as lawyers in private practice or business. But less capable conservatives/libertarians, particularly those on the low end of the distribution of ability, would be attracted to legal academia…but that’s not what we find.

The Interest Hypothesis is harder to get at with this data, but I think something can be said. If fewer conservatives/libertarians are interested in being a professor (not because of hostility, real or perceived, due to discrimination, but less academically inclined), and the Brainpower Hypothesis is not implicated, then the ability of conservatives/libertarians and others should have overlapping distributions, and the distributions of Interest and Brainpower should be uncorrelated. Thus, only conservatives/libertarians at the high end of the Interest distribution would go into academia. But they should not be distinguishable from non-conservatives/libertarians on ability or performance since that is uncorrelated from Interest.

He also notes the flaw with the Interest hypothesis:

Thus, while conservatives/libertarians may be able to match their peers on Brainpower, they’re generally just squeaking in the door with Interest, and since law professor success is a combined function of both, they will be on the lower end of the distribution of measured success.

But that is not the case—on average they publish more and are cited more than their peers at statistically significant levels. One could posit that the distribution of Interest among conservatives/libertarians is bimodal, with the high-interest group shifted to the right of non-conservatives/libertarians, resulting in them outperforming their peers. But such a distribution seems unlikely and there’s no empirical or theoretical explanation for (a) bimodal distribution of Interest; and (b) one group to have a bimodal distribution and the other to have a normal one.

You can read the rest of his response here.