Anyone familiar with psychology has probably heard a statement like this: A significant percentage of male & female undergraduates displayed X when prompted by Y. And typically the conclusion of the study is something like: So humans display X in the presence of Y. Taking the behavior of undergrads and extending it to all of humanity is an intriguing leap, right?

To be fair, for research purposes, undergrads are cheap and accessible. But, as noted by the blogger Headcase, such terms are better used to describe a hot date rather than good data.

Well, a group from the University of British Columbia recently published an enormous meta-analysis on the danger of assuming that all of humanity closely matches the behaviors of 20-something college students. They cite evidence that between 2003 and 2007 undergrads made up 80 percent of study subjects in six top psychology journals, and that 96 percent of all psychology samples come from countries that make up only 12 percent of the world’s population. They call this the WEIRD population—Western Educated Industrialized Rich Democratic—and say that they are the least representative populations one could find for generalizing about humans.

The researchers found huge variability between global populations along measures of motivation, self-perception, reasoning, heritability of IQ and even visual perception. For instance the Müller-Lyer visual illusion, which shows two lines of equal length where one is often perceived, at least by American undergrads, as longer than the other, is actually not an illusion at all for the San foragers of the Kalahari. The authors also note points of similarity like this one: in 37 populations, males tend to rank physical attractiveness of mates to be more important than do females.

The main plea from the researchers is that far too often these so-called WEIRD populations are actually the "outliers" and psychologists need to be less cavalier about labeling some behavior as human nature based on the desires, emotions and culture of a group of 19-year old co-eds.

—Christie Nicholson

(Editor's Note: To explore more of the data, the paper’s authors suggest this blog post: http://neuroanthropology.net/2010/07/10/we-agree-its-weird-but-is-it-weird-enough/ )