Sam Nelson at Catching Flies has an interesting question about the liberal professors study. You should read his whole post if you're interested:
OK, their data comes from a survey completed in 1999 where they find 72% of professors are "left/liberal" and only 15% "right/conservative." About 13% must be something else. They compare this to a Carnegie report from 1984 showing a 39 - 34 % split between liberals and conservatives and this is the basis for their claim that there has been a shift. Well, a shift in the ideological orientation of faculty is ONE explanation of this data, but it is not the only one. This would be a huge shift in merely 15 years, but it could just as easily be an indication that their 1999 data is seriously flawed and their results atypical. What happened in those 15 years to explain a shift like they suggest? While there was significant replacement in most faculties during the period 1984 to 1999, a lot of the people who were around in 1984 were still on faculties in 1999. Did they suddenly become liberal, or did only conservatives retire? A change this large has to be explored and a variety of explanations considered before we can draw the kinds of conclusions Rothman et al draw.
In other words, there's more than one explanation for the difference between the 1984 data and the 1999 data. The authors of the study need to address that.
Heather will have more to say about the whole study later.
If you're really interested, you should go read the article at Inside Higher Ed and the comments on the article. They present a very interesting discussion.