In my last two posts, I put forward some reasons why Gross and Simmons' important new paper on academic ideology understates the prevalence of liberals in academia. It is only fair to also point out a way in which that study overstates that prevalence, or at least underestimates the proportion of non-liberal academics. It does so by collapsing academics' ideologies into three categories along a single continuum: "liberal," "conservative," and "moderate." Respondents to their ideology question had the option of describing themselves as "Very liberal," "liberal," "slightly liberal," "middle of the road," "slightly conservative," "conservative," or "very conservative."

Note that this one-dimensional ideological scale entirely ignores libertarians, who - roughly speaking - are "liberal" on social issues, and "conservative" on economic ones. Some libertarians may describe themselves as "conservative" on the Gross-Simmons scale. Others, however, might pick "liberal" or "middle of the road," or simply choose not to answer the question because they don'e see a choice they like. For example, if I average out my "liberal" positions on social issues with my "conservative" ones on economic issues, I could describe myself as "middle of the road" on average. But it's a very different kind of "moderation" from that associated with, say, DLC Democrats.

Ignoring libertarians may be defensible in studies of the general population, where they are relatively rare (although even among the general public, some evidence suggests that about 10 percent are closer to being libertarian than conservative, moderate, or liberal). It is much more problematic in a study of academics, where libertarians are a much larger fraction of the nonliberal total than in the general public. In my experience, about half of nonliberal/noncentrist law professors are in fact libertarians rather than social conservatives. Lawprofs are not included in the Gross-Simmons study. But economists and political scientists (two other groups with which I have some familiarity) are, and the libertarian-conservative ratio there does not seem to me much different than that in law. Even if we cautiously assume that libertarian academics are only half as common as conservative ones, the Gross-Simmons data imply that about 5% of academics are libertarians (vs. 9.4% conservative). And another 5% would be "slightly libertarian" (vs. 10.5% "slightly conservative").

How much does this skew Gross and Simmons' overall results? It is difficult to say. It all depends on how many libertarian academics would describe themselves as "conservative" or "very conservative" when they answered the author's one-dimensional ideology question and how many would describe themselves as "liberal," falling into one of the three categories the authors classify as "moderate," or simply refuse to answer the question. Given the deepening of the conservative-libertarian split during the Bush years, I suspect that the proportion of libertarians willing to embrace the "conservative" label has been declining; this trend is likely to be unusually strong among academics, most of whom follow politics closely. My best guess - and it's only a guess - is that about 50-70% of libertarians would refuse to embrace the two most "conservative" categories in the Gross-Simmons framework. Assuming that libertarian academics make up about 6-7% of the total (perhaps an underestimate), that implies that the true proportion of right of center academics is 12-13% rather than the 9% that the authors estimate. In some fields, such as economics and other social sciences, the proportion of libertarians among the nonliberals is likely to be significantly higher than that. If you count the putative "slightly libertarian" academics (parallels to the authors' "slightly liberal" and "slightly conservative" categories), the libertarian proportion would be about twice as high, perhaps 10-14% of the total sample.

In my judgment, properly accounting for libertarians would not overturn the conclusion that the left side of the political spectrum is overwhelmingly dominant in academia - especially when you consider the factors discussed in my previous two posts. It would, however, substantially increase the estimated proportion of academics who are neither liberal nor "moderate."

UPDATE: I was remiss in not mentioning this 2005 study of social scientists' political views by GMU economist Daniel Klein and Swedish scholar Charlotta Stern, which finds that "social scientists who deviate from left-wing views are as likely to be libertarian as conservative." This finding strengthens the case for including libertarianism as a separate category in studies of academic ideology.