Science v. bias

News from last week which could prompt sociologists to mutter "I told you so". [But let's face it: that doesn't take much, does it? ;) Yours faithfully, An Ex-Sociology Student.]

A study by Janet Shibley Hyde of the University of Wisconsin in Madison finds that many psychological gender differences depend on the context in which they’re measured. On most psychological variables, men and women, boys and girls are alike.

In one study where participants in the experimental group were told that they were not identified as male or female nor wore any identification, neither sex conformed to a stereotyped image when given the opportunity to act aggressively. They did the opposite to what was expected.
- press release, American Psychological Association

For me the most interesting part of this study is found in something it quotes:

Another important reviewer of gender research in the early 1900s, Helen Thompson Woolley (1914), lamented the gap between the data and scientists' views on the question: The general discussions of the psychology of sex [ie. gender], whether by psychologists or by sociologists show such a wide diversity of points of view that one feels that the truest thing to be said at present is that scientific evidence plays very little part in producing convictions.

Is the conviction of this latest study justified by evidence? I've got no idea. I don't understand the statistics used, and I'm not even clear about the method (a review of meta-analyses of previous research? Just how far away are the actual experiments with actual people?) But the thing is this: for decades we've all been led to believe that men and women are psychologically different. If the findings of this latest study are correct - that males and females are similar in not all but most psychological variables - then how did the theory of difference persist for so long?