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Mr. Inbar and Mr. Lammers, who were at the conference, couldn’t believe that there were really so few conservatives in their field. A month or two after Mr. Haidt’s talk, the two researchers were having a few beers and decided to design a survey examining their colleagues’ political beliefs.

Beyond their findings on discrimination, the pair determined that while conservatives are minorities in their field, they are not statistically negligible: About 40 percent of respondents identified themselves as moderate or conservative on economic issues, while 30 percent did so on foreign policy issues. The widest divide occurs on social issues, the contested terrain in the culture wars shaking the academy. On these contentious issues, 90 percent identified as liberal and only 4 percent as conservative.

“As offensive as it may seem to many social psychologists,” Mr. Inbar and Mr. Lammers write, “believing that abortion is murder does not mean that one cannot do excellent research.” To think otherwise, they argue, damages the scientific credibility of psychology — a field that has been criticized in the press for being a pseudo-science.

The statistical representation of self-reported conservatives in the study may be largely moot as long as they are intimidated by a hostile, discriminatory majority. After all, a silent minority can hardly function as the kind of check on the prevailing assumptions of their liberal colleagues essential for robust academic debate.

“Because of the way the confirmation bias works,” Mr. Haidt says, referring to the pervasive psychological tendency to seek only supporting evidence for one’s beliefs, “you need people around who don’t start with the same bias. You need some non-liberals, and ideally some conservatives.”