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It's a golden age for the study of human nature. Almost every week brings new discoveries that shed light on why we behave the way we do. A vast new field of academic endeavour has revealed how people are subtly influenced by environmental cues and unconscious biases, and why our willpower often fails us despite our best efforts.

For example, why is there an achievement gap in math between men and women? Social psychologists believe a major reason is something called "stereotype threat." The theory is that if you think there's a negative stereotype about you or your social group (you are bad at X), you'll choke and do worse. In other words, women perform worse in math because they think they're expected to. Stereotype threat, the leader of one recent study warned, "has major implications for women in technology and business environments, where women's abilities are regularly impugned by negative stereotypes."

Stereotype threat is one of the most famous and influential ideas in psychology. It is thought to be a key explanation for group differences in performance – whether the group is defined by gender, race or class. But now, stereotype threat itself is under threat. New studies are questioning just how robust it is, and even whether it exists at all. The same goes for many other staples of social psychology – to the point where the whole edifice is tottering badly.

The bombshell came last August, after an inquisitive scientist at the University of Virginia, Brian Nosek, launched something called the Reproducibility Project. It was designed to test how reliable psychology studies really are. Hundreds of researchers replicated 100 published psychological experiments to see if they could get the same results. Their success rate was a dismal 36 per cent. There's been a lot of squabbling over those results. But the Reproducibility Project was just the latest in a string of doubts and scandals that have plagued the field. And now, a lot of people, including scientists who have invested years of their professional lives in these theories, feel as if they're in a train wreck.

"Sometimes I wonder if I should be fixing myself more to drink," Michael Inzlicht, a leading social psychologist at the University of Toronto, wrote recently in a lengthy blogpost. You can't blame him. Prof. Inzlicht is an expert in the nature of self-control and willpower – another red-hot area in psychology.

The prevailing theory is that willpower is a finite resource, like Daniel Engber writes, "a muscle that can be exercised to exhaustion". This is among the most widely accepted findings in social psychology. But is it true? Maybe not. Prof. Inzlicht was part of a replication team that chose one classic experiment on the depletion theory of willpower, and repeated it in 24 different labs. And what they found was – nothing. Only three of the labs produced any significant result at all, and one of those was negative.

Prof. Inzlicht's cri de coeur quickly went viral. "Have I been chasing puffs of smoke for all these years?" he wrote. "… What other phenomena, which we now consider obviously real and true, will be revealed to be just as fragile? As I said, I'm in a dark place. I feel like the ground is moving from underneath me and I no longer know what is real and what is not."

How could so many scientists be so wrong? It's not hard to find the answers. First, there's publication bias. Publication is essential to every scientist's career, and neat, tidy, interesting results are far more likely to be published than messy, murky ones. "The overwhelming bias is to publish positive results, the more striking the better," Yoel Inbar, a colleague of Prof. Inzlicht, told me. "So when you get a negative result, you just throw it in the file drawer." A string of high-profile, sexy results has a huge influence on hiring, tenure and research grants.

It's also easy for researchers to fiddle the results by tweaking the statistical analysis. They may not mean to, but they do. With enough flexibility, you can find just about anything – as one wag showed when he "proved" that listening to a Beatles song makes you younger.

Social psychology has another big problem: a massive leftward tilt. In the past 20 years, the field has become an ideological monoculture. Jonathan Haidt, one of the most respected voices in the field, argues that the rapid loss of political diversity poses an existential threat second only to the replication crisis. Research into politically controversial topics becomes unreliable, because politically favoured conclusions get a pass while politically unpalatable conclusions get rejected.

What can be salvaged from the wreckage? It may take years to find out. "At some point," Prof. Inzlicht recently told Slate magazine, "we have to start over and say, This is Year One."

Editor's Note: An earlier version of this column did not attribute the phrase "a muscle that can be exercised to exhaustion" to Slate writer Daniel Engber. The Globe and Mail apologizes to Mr. Engber. This online version has been corrected with the proper attribution.

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