Men ARE From Mars, After All! And Women From Venus, Duh

So tells a new study about gendered personality differences:

Men and women have large differences in personality, according to a new study published Jan. 4 in the online journal PLoS ONE.

The researchers used personality measurements from more than 10,000 people, approximately half men and half women. The personality test included 15 personality scales, including such traits as warmth, sensitivity, and perfectionism. When comparing men's and women's overall personality profiles, which take multiple traits into account, very large differences between the sexes became apparent, even though differences look much smaller when each trait is considered separately.
However, the study indicates that previous methods to measure such differences have been inadequate, both because they focused on one trait at a time and because they failed to correct for measurement error.
The authors conclude that the true extent of sex differences in human personality has therefore been consistently underestimated.

Indeed, the study (available here) finds that men's and women's personalities might overlap by as little as ten percent! Depending on what statistical manipulation the researchers used.

I have read the study, but the particular method the authors used to get from pretty small average differences on the individual character traits to a humongous overall difference is not one that I know well. But others have criticized the method:

But the findings counter the prevailing view among psychologists that, on the whole, men and women are more similar than they are different, in a number of ways, including personality traits.
Janet Shibley Hyde, a professor of psychology and women's studies at the University of Wisconsin who published a paper in 2005 that was influential in contributing to this hypothesis, said the new study does not overturn this view.
For starters, the men and women in the study assessed their own personality traits. People may be inclined to rate themselves in a way that conforms with gender stereotypes, Hyde said. "It's not very manly to say that you're sensitive," she said.
Hyde also said using the 15 personality facets to compute a "global difference" gives you a value that doesn't have any actual meaning.
"It's really uninterpretable, it doesn't mean anything," Hyde said.
In addition, the way the researchers crunched their numbers biases their results, because their method maximizes the differences between males and females, Hyde said.
Patrick Ian Armstrong, a professor of psychology at Iowa State University, agreed with Hyde's assessment. Armstrong pointed out that the "global difference" value will actually get bigger the more personality factors the researchers consider (so analyzing 15 factors will show a greater difference than analyzing five factors.)
Given the issues with the study's methods, "it's not as open and shut a case as they make it out to be," Armstrong said. "The questions they're trying to answer are probably still worth asking," Armstrong said.

I hope that other researchers in the field explain these "novel" methods better for the general audience. Right now all I get is that the authors argue other people manipulate survey data on gender differences in character traits wrong whereas they manipulate it right. Right!

And what might the implications of this study be? One of the authors, Paul Irving:

"Psychologically, men and women are almost a different species," said study researcher Paul Irwing, of the University of Manchester, in the United Kingdom.
The new findings may explain why some careers are dominated by men (such as engineering) and others by women (such as psychological sciences), Irwing said.
"People self-select in terms of their personality… and what they think is going to be suitable in terms of the fit," for their career, Irwing said.

I LIKE that different species argument! The radical feminist segregationists are right, after all.

More seriously, note how we get from small average differences on fifteen scales to humongous statistically created overall differences. Even more seriously, note the political use to which the results are intended. Finally, and not at all seriously, note that Paul Irwing must have a female personality, to work in psychology.

The lead researcher of the study, Marco Del Giudice, describes his research interests as follows:

My main research area is the evolutionary study of human development across the life span. This is an exciting and rapidly growing field, rife with opportunities for theoretical synthesis and interdisciplinary integration. My research interests cover a wide range of topics, from attachment and parent-child relations to personality and psychopathology; indeed, the evolutionary paradigm cuts through the traditional disciplinary boundaries, revealing psychology as a unified scientific endeavor and the human life course as an integrated whole. A common thread underlying much of my current work is the application of life history theory and sexual selection theory to the study of individual and sex differences in attachment, mating, social competition, and personality. A related topic is the evolution of developmental stages and transitions.

So that's the theoretical background for the study (which seems to have had a test-run in Evolutionary Psychology, 2009). It's based on evolutionary psychology. Nothing wrong with that, of course, as long as the readers remember that biologically determined sex differences are one of the core pillars of one particular kind of evolutionary psychology.

From that comes the idea that women are inherently suited for certain occupations and not others, that cultural norms are irrelevant and environmental effects ignored.

All that is worth thinking about, as is the fact that this study is reported all over the place with that "Mars/Venus" argument and often pictures of a man and a woman arguing*. This stuff really sells. Sadly, corrections to this stuff do not sell.

But ultimately my reaction to the study is really based on something completely amateurish: No way are men's and women's personalities so different that they only overlap in ten or eighteen percent of the cases! If that really was the case we would all know it**. So there is something odd about the methods and the numbers they produced.
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*For one example, check out this one. It crops the criticism of the study, too.
**Think of the height difference among men and women. Not sure what the percentage overlap in the height distributions is but it's unlikely to be anywhere near as small as the created measures in this study. My point is that something so humongous would be common knowledge.

Added later: Here is Janet Hyde's response to the article.