http://www.theesa.com/facts/pdfs/ESA_EF_2011.pdf
But how reliable it is? Who did they ask? And how are the genders distributed among each community or kind of game? Because there's a huge difference between facebook, Xbox live and what we have here.
Some thoughts:
1) The more involved the hobby is, the less women in it. There are relatively few women in retrogaming, wargaming, and train games and most gaming blogs are made by men.
2) If a community is rooted in the arcades, there will be very few women in it.
3) The amount of women is proportional to the niceness of the community. I think this ties to 1) in that the more bullshit the community has, the more you have to work just to have fun. Niceness also affects the apparent number of women as they start turning down their mics to not be yelled at by 13 year olds which, of course, reduces the overall niceness.
This is very apparent in TF2: You will see women talking only in the good servers, never in a bad one.
4) It seems there are many women playing pen and paper RPGs, which is surprising in that it's one of the most involved parts of gaming. However, it's a very narrative artform and if fanfiction is any proof, narrative tends to gather female players.
Let's see where this goes

VVV