What I would call gamer is somebody which dedicate quite a sizable part of his life to play video game (whether you see that negatively or positively). If you reduce it "playing some video game sometime" you get a pretty vaccuous statistic where pretty much everybody is inside. It is equivalent to calling "gambler" anybody which made a bet of any sort (casual or not) at *ANY* point in 2014. Pretty much not what is named a gambler , and so that should not be used for gammer either.
ALso video game are severly segmented. They target by segment. Dude-bro setgment (COD, battlefield), sport segment, FPS twitch competition , MOBA segment, MMO segment, single player and "retro" segment, etc... None of those segment have the same appeal to everybody. As such saying 52% of gamer are girl is utterly useless as 1) this says nothing about targeted segment 2) you lowered the "is gamer" definition until everybody is in, so it is useless to targeting.
The fact remain is that even among my numerous nephew and niece, the young segment, *girl* in average might play a game more, but disparage and persiflage against boy which still play a lot more. Sure it is anecdotal, but that's more people than some small scale psychological study use. They do not see themselves as gamer, because most of them rightfully recognize it not as "has played a video game ocne in 2014" but rather "has made a major hobby of playing video game".
That said the proportion of "gamer" aka people making it a hobby and playing numerous hours during the week, is increasingly populated by women. I welcome that because I have been tired of the AAA game for a decade or so (too many which are dude-bro shoota-shoota , women with extremly skimpy clothing, white dude with surging muscle, damsel in distress and male hero which snaps the finger and get the girls ---- where are the beyond good and evil and the world with an heroine ?) and hope to see a surge in different gaming type as women rise to be the fabled 50+%. True to be said there is a much more diverse gaming offer today than there was 10 years ago thanks to indy.