PHOTOGRAPH BY SCOTT F. SMITH/THE NEW YORK TIMES/REDUX

On January 27, 2011, from a stage in the middle of the San Antonio Convention Center, Jonathan Haidt addressed the participants of the annual meeting of the Society for Personality and Social Psychology. The topic was an ambitious one: a vision for social psychology in the year 2020. Haidt began by reviewing the field that he is best known for, moral psychology. Then he threw a curveball. He would, he told the gathering of about a thousand social-psychology professors, students, and post-docs, like some audience participation. By a show of hands, how would those present describe their political orientation? First came the liberals: a “sea of hands,” comprising about eighty per cent of the room, Haidt later recalled. Next, the centrists or moderates. Twenty hands. Next, the libertarians. Twelve hands. And last, the conservatives. Three hands.

Social psychology, Haidt went on, had an obvious problem: a lack of political diversity that was every bit as dangerous as a lack of, say, racial or religious or gender diversity. It discouraged conservative students from joining the field, and it discouraged conservative members from pursuing certain lines of argument. It also introduced bias into research questions, methodology, and, ultimately, publications. The topics that social psychologists chose to study and how they chose to study them, he argued, suffered from homogeneity. The effect was limited, Haidt was quick to point out, to areas that concerned political ideology and politicized notions, like race, gender, stereotyping, and power and inequality. “It’s not like the whole field is undercut, but when it comes to research on controversial topics, the effect is most pronounced,” he later told me. (Haidt has now put his remarks in more formal terms, complete with data, in a paper forthcoming this winter in Behavioral and Brain Sciences.)

Haidt was far from the first to voice concern over the liberal slant in academia, broadly speaking, and in social psychology in particular. He was, however, the first to do it quite so visibly—and the reactions were vocal. At first, Haidt was pleased. “People responded very constructively,” he said. “They listened carefully, took it seriously. That speaks very well for the field. I’ve never felt as if raising this issue has made me into a pariah or damaged me in any way.” For the most part, his colleagues have continued to support his claims—or, at least, the need to investigate them further. Some, however, reacted with indignation.

The critique started with data. True, there was little doubt that conservatives in the world of psychology are few. A 2012 survey of social psychologists throughout the country found a fourteen-to-one ratio of Democrats to Republicans. But where were the hard numbers that pointed to bias, be it in the selection of professionals or the publication process, skeptics asked? Anecdotal evidence, the Harvard psychologist Daniel Gilbert pointed out, proved nothing. Maybe it was the case that liberals simply wanted to become professors more often than conservatives. “Liberals may be more interested in new ideas, more willing to work for peanuts, or just more intelligent,” he wrote. The N.Y.U. political psychologist John Jost made the point even more strongly, calling Haidt’s remarks “armchair demography.” Jost wrote, “Haidt fails to grapple meaningfully with the question of why nearly all of the best minds in science find liberal ideas to be closer to the mark with respect to evolution, human nature, mental health, close relationships, intergroup relations, ethics, social justice, conflict resolution, environmental sustainability, and so on.”

The views on the other side are equally strong. When I asked Paul Bloom, a psychologist at Yale who edits the journal where Haidt’s paper will appear, what he thought of the research, he pointed out what he believed to be a major inconsistency in the field’s responses. “There’s often a lot of irony in this area," he said. "The same people who are exquisitely sensitive to discrimination in other areas are often violently antagonistic when it comes to political ideology, bringing up clichéd arguments that they wouldn’t accept in other domains: 'They aren’t smart enough.' 'They don’t want to be in the field.' ”

The Nobel Prize-winning behavioral economist Daniel Kahneman called Haidt’s work “great” and “a real service.” The University of British Columbia psychologist Steven Heine pointed out, “Science benefits from diverse perspectives, and key advances often occur when ideas slip across disciplinary borders. But many invisible norms and practices in a field can discourage the mingling of diverse ideas.” Political homogeneity, he went on, comes at “a substantial cost” to research quality. Conservative viewpoints, the Florida State University psychologist Roy Baumeister added, “would inform and elevate how we understand a huge part of life and of culture.”

So, apart from generating strong emotions, what do the data actually say?

A year after Haidt’s lecture, the Tilburg University psychologists Yoel Inbar and Joris Lammers published the results of a series of surveys conducted with approximately eight hundred social psychologists—all members of the Society for Personality and Social Psychology. In the first survey, they repeated a more detailed version of Haidt’s query: How did the participants self-identify politically? The question, however, was asked separately regarding social, economic, and foreign-policy issues. Haidt, they found, was both wrong and right. Yes, the vast majority of respondents reported themselves to be liberal in all three areas. But the percentages varied. Regarding economic affairs, approximately nineteen per cent called themselves moderates, and eighteen per cent, conservative. On foreign policy, just over twenty-one per cent were moderate, and ten per cent, conservative. It was only on the social-issues scale that the numbers reflected Haidt’s fears: more than ninety per cent reported themselves to be liberal, and just under four per cent, conservative.

When Inbar and Lammers contacted S.P.S.P. members a second time, six months later, they found that the second element of Haidt’s assertion—that the climate in social psychology was harsh for conservative thinkers—was on point. This time, after revealing their general political leanings, the participants were asked about the environment in the field: How hostile did they think it was? Did they feel free to express their political ideas? As the degree of conservatism rose, so, too, did the hostility that people experienced. Conservatives really were significantly more afraid to speak out. Meanwhile, the liberals thought that tolerance was high for everyone. The more liberal they were, the less they thought discrimination of any sort would take place.

As a final step, the team asked each person a series of questions to see how willing she would personally be to do something that could be considered discrimination against a conservative. Here, an interesting disconnect emerged between self-perception—does my field discriminate?—and theoretical responses about behaviors. Over all, close to nineteen per cent reported that they would have a bias against a conservative-leaning paper; twenty-four per cent, against a conservative-leaning grant application; fourteen per cent, against inviting a conservative to a symposium; and thirty-seven and a half per cent, against choosing a conservative as a future colleague. They persisted in saying that no discrimination existed, yet their theoretical behaviors belied that idealized reality.

Haidt hadn’t planned on continuing his research after his initial speech. He had meant to raise the issues and wait for others to take over. But, two months after the convention, he came across the thoughts of a libertarian graduate student (now a co-author of Haidt’s new paper), published on the S.P.S.P. listserv. José Duarte hadn’t been at the S.P.S.P. meeting, he told me when we spoke. But the subsequent attention sparked his interest. He had long been fascinated by the methodological issues that stemmed from a lack of political skepticism in the field, and he also believed that he had been rejected from one graduate program because of his political views. Duarte has written about that experience, and Haidt has compiled a list of other student accounts on his personal Web page. The problem, Haidt decided, was widespread enough that it merited further research.