A study recently done by the Entertainment Software Association (ESA) claims that 38% of American gamers are female. I could no find any links to the actual study, and a Google search returned nothing. The closest I got was a Game Player Data page on the ESA website.
I don’t find anything wrong with the study itself, but the response from people who see the results are a bit moronic sometimes. Just look at the headline for the Kotaku link I have above: Stuff We Already Know About Female Gamers: Now In A Study! Why do people keep saying that women gamers are more casual compared to their male counterparts? Guess what, there are a lot of casual male gamers too! It’s like saying hardcore female gamers are an anomaly, while casual male gamers aren’t that strange at all.
There is a lot more behind the statistics than just numbers. The results of this study definitely should not be interpreted as female gamers mostly play casual games because they are female.