It is widely believed that the numbers gap between men and women in public opinion forums results from women's hesitancy - be it culturally imbued or inherent - to assert themselves in venues traditionally dominated by men. But this theory of the gender gap is experiencing a complication: As it turns out, women shy away even from asserting themselves anonymously. Despite the fact that Wikipedia is a young forum with no patriarchal tradition, and despite contributor anonymity, a study carried out by the Wikimedia Foundation last year found that a mere 13 percent of contributors to the crowd-sourced encyclopedia are women.

Sue Gardner, the executive director of the foundation, told the New York Times that the contributor gender breakdown has produced a noticeable bias in the encyclopedia toward topics likely to be of greater interest to men. For example, friendship bracelets, Sex and the City, and Mexican feminist writers all get short-changed by the website in comparison to its articles on baseball cards, The Sopranos, and characters in The Simpson's, respectively. Thus Gardner believes increasing the number of female contributors is a necessity: the quality of Wikipedia is suffering without them.

Gardner and the Wikimedia board of directors have set the goal of upping the female contribution to 25 percent by 2015; before tackling the question of how to do it, though, they must first figure out why the numbers are what they are in the first place.

According to the OpEd Project, a New York-based organization that monitors gender gaps, the Wikipedia gender gap is similar in degree to that of other "public thought-leadership forums." A man/woman ratio of 85-to-15 is common in government bodies and in newspaper op-ed columns, for example. But in an open-ended forum where loud, aggressive, or competitive men cannot be blamed for shutting women out, why should a gender gap exist? Why are women staying quiet on Wikipedia?

No one is quite sure, but Catherine Orenstein, founding director of the OpEd Project, believes it stems from an inherent lack of confidence women have about their own knowledge and viewpoints. Her group urges women to shift their focus away from themselves and their insecurities, and "turn the focus outward, thinking about the value of [their] knowledge."

Or perhaps women simply aren't as drawn to online communities, or to fact and trivia-gathering, as men are. It's an open question.

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Follow Natalie Wolchover on Twitter @nattyover