When social psychologist Jonathan Haidt famously polled his fellow academics for their political leanings at the 2011 convention of the Society for Personality and Social Psychology, only 3 hands out of a thousand were raised in response to his query about conservative leanings. Just three. As the New York Times reported:

“This is a statistically impossible lack of diversity," Dr. Haidt concluded.... "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.”

Harvard University psychologist Daniel Gilbert very open-mindedly generated one such alternate explanation for the paucity of conservative social psychologists:

[L]iberals may be more interested in new ideas, more willing to work for peanuts, or just more intelligent, all of which may push them to pursue the academic life while deterring their conservative peers.

Well, yes that is one possibility. However, a new study, "Political Diversity in Social and Personality Psychology," by Dutch psychologists finds that overt discrimination against conservatives [PDF] likely plays a role. The researchers surveyed several hundred social psychologists, most of them American, and found that 6 percent identified as "overall conservative" - certainly better than 3 in a 1,000 but nowhere near being representative of the larger population. The researchers then ask:

Why, then, did Haidt have such difficulty finding more than a handful of conservative colleagues? The current results suggest one answer: Members of the conservative minority are reluctant to express their political beliefs publicly. Survey 2 shows why: Hostility toward and willingness to discriminate against conservatives is widespread. One in six respondents said that she or he would be somewhat (or more) inclined to discriminate against conservatives in inviting them for symposia or reviewing their work. One in four would discriminate in reviewing their grant applications. More than one in three would discriminate against them when making hiring decisions. Thus, willingness to discriminate is not limited to small decisions. In fact, it is strongest when it comes to the most important decisions, such as grant applications and hiring.

This hostile climate offers a simple explanation of why conservatives hide their political opinions from colleagues. Given that all academics depend on the opinions of their colleagues—who judge their papers, grants, and job applications—and given that such judgments are typically made by multiple reviewers (most of whom are liberal), this means that outspoken conservatives face a very serious problem. Hence, the more conservative respondents are, the more they hide their political opinions.

Conservatives stay quiet (or stay out of academic psychology altogether) because they don't want the thundering herd of independent minds to stampede their careers into the dust.