Should We Be Surprised at Political Bias in Academia?

Ruh-Roh. John Tierney in today’s Times:

… Jonathan Haidt, a social psychologist at the University of Virginia who studies the intuitive foundations of morality and ideology … polled his audience at the San Antonio Convention Center [during the annual meeting of the Society for Personality and Social Psychology], starting by asking how many considered themselves politically liberal. A sea of hands appeared, and Dr. Haidt estimated that liberals made up 80 percent of the 1,000 psychologists in the ballroom. When he asked for centrists and libertarians, he spotted fewer than three dozen hands. And then, when he asked for conservatives, he counted a grand total of three.
“This is a statistically impossible lack of diversity,” Dr. Haidt concluded, noting polls showing that 40 percent of Americans are conservative and 20 percent are liberal. In his speech and in an interview, Dr. Haidt argued that social psychologists are a “tribal-moral community” united by “sacred values” that hinder research and damage their credibility – and blind them to the hostile climate they’ve created for non-liberals.
“Anywhere in the world that social psychologists see women or minorities underrepresented by a factor of two or three, our minds jump to discrimination as the explanation,” said Dr. Haidt, who called himself a longtime liberal turned centrist. “But when we find out that conservatives are underrepresented among us by a factor of more than 100, suddenly everyone finds it quite easy to generate alternate explanations.”

The lack of diversity isn’t actually “statistically impossible” in a self-selecting group. But that of course is the point. How can it be that an academic field is so politically homogeneous? What kind of biases does such homogeneity produce? What sort of ideas get crowded out? And how homogeneous are other disciplines?
I have to say that I was surprised at the overt political (leftward) bias exhibited by several prominent economists at the recent American Economics Association meetings, although my sample set was quite small.
It is interesting — and sobering — that two fields, psychology and economics, that we rely upon to describe and amend bias in the world are themselves so susceptible to bias within the ranks of their practitioners.
Addendum: here’s a link to Daniel Klein‘s ongoing survey about policy views within academia (HT: JBriggerman)