PSYCHOLOGY FINDS itself in the midst of a major media renaissance: bestselling books, popular magazine stories, blog posts that go viral. The public cannot get enough.

Yet among researchers, there is a dawning awareness of a potentially serious issue at the core of what they do. The experiments that offer so many insights and takeaways might be seriously flawed — the result of relying on too homogenous a sample. The engine of science runs on the fuel of experiments. If you are interested in conducting psychology experiments, you need people. And if you are a researcher at a university there is an obvious solution, the sea of undergrads right on campus.

One survey of top journals by a researcher at Clark University found that two-thirds of the studies used American psychology undergrads as their sole subjects. This means that grand claims about human nature are based on the behavior of a narrow group of educated, relatively wealthy people at a particular moment in their lives.

Put another way, the subjects of psychology are WEIRD — they are Western and Educated, and they come from Industrialized, Rich, and Democratic societies, says University of British Columbia scholar Joseph Henrich. Working with two colleagues, he has found strong evidence that human psychology varies around the planet in fundamental ways.

For example, one of the lessons of modern psychology is that people work hard, sometimes unconsciously, to maintain a positive image of themselves; another is that most people tend to rate their own abilities as above average. But when you venture into other societies, these effects fade or disappear. It turns out that in these ways, and in many ways, the psychology of Americans is at the extreme edge of a spectrum, and that the only group which is even more of an outlier is a strange tribe known as the American undergraduate.

Many studies use American psychology undergrads as their sole subjects — meaning that grand claims about human nature are based on a narrow group of educated, relatively wealthy people at a particular moment in their lives.

“If there was one group you wouldn’t want to use” to understand human psychology, says Henrich, “it would be American undergraduates.”

The differences run deep. The WEIRDos of the world differ in the way they conceive of themselves, in what they consider fair, in how much they value choice, and, quite literally, in how they see the world. There is a well-known illusion, in which one line appears longer than another, even though they are the same length. It was thought that the illusion was just a part of the way that perception works. But show it to someone like a San forager of the Kalahari, and there is no illusion. If something as basic as how the brain processes vision can be so different, one can only imagine the potential differences in, say, how someone makes a decision.

This is of more than academic concern. In recent years, there has been a commendable move to use the insights of the behavioral sciences to improve not only ourselves but our societies. The aim now is to improve institutions — to make public schools run better, for example, or to alleviate poverty and other social ills. But psychology’s WEIRD problem suggests that these practitioners must move ahead with extreme care. People in the real world may not react the same way as psych students at an East Coast university.

“These policies don’t just apply to undergrads, so that gives you an incentive to understand things more generally,” says Harvard University researcher David Rand.

Rand recently started to pursue a fascinating solution. He uses a software platform, Amazon’s “Mechanical Turk,” which allows people from around the world to sign in and perform easy tasks. This gives him an inexpensive way to run experiments online using volunteers from around the world. It’s not perfect — it only includes fairly savvy Internet users who speak English — but he tells me that in experiments on moral reasoning, he is already seeing hints that established results using American undergrads don’t hold up.

Clearly, though, psychology as a field needs to do more of the hard work of testing its ideas in other contexts, beyond the relatively fast and easy experiments you can do down the hall. And the fact that others think differently is not so much a problem for psychology as it is an opportunity — a chance to come to a deeper understanding of the diversity of the mind.