In a 2013 survey cited in the above Destructoid article, 15% of a demographic sample of 40,000 MMO players were women.
42% of all gamers are women (ESA, 2011).
Another survey around the same time found women counted as 40% of the MMO/MOBA( 24% of overall) category – http://www.joystiq.com/2014/10/23/league-of-legends-tops-mmo-revenue-list-hearthstone-no-10/
There’s an interesting Reddit post on ‘assumed to be female’ avatars – http://www.reddit.com/r/swtor/comments/1jie39/assumed_to_be_female_personal_experience/
A 2011 poll found 57% of MMO female players to be married – http://www.swtor-life.com/editorial/is-“she”-really-a-“she”-female-gamers-and-gender-bending-in-mmorpgs-by-daelda/4233/
In 2009, women made up 20% of Everquest II players – http://dmitriwilliams.com/lfgpaperfinal.pdf
A previously indirectly cited 3 year survey ending in 2006 found women players of MMORPGs counted as the majority in all age cadres above 23 – http://www.nickyee.com/pubs/Yee%20-%20MMORPG%20Demographics%202006.pdf – with only 27% of female gamers having come into gaming through a romantic partner, though 59.8% played with one.
The same survey also found that women prefer games with opportunities to relate to other characters and players. Possibly as a result, women players held more close in-game friends.
Another survey by the same author found that women weight Character Creation, Landscape and Quests as the most heavily preferred game elements. For men it was Character Creation or Quests at the top (depending on Age) and the combat system towards number 2 or 3.
In the same study, it was shown that women prefer First Person Perspectives while men prefer 3rd. http://www.gamasutra.com/view/feature/130552/unmasking_the_avatar_the_.php?print=1
Notably (towards your beta testers question), among MMO players women are *significantly* less likely to abandon current MMO games for new ones.
I was interested in SWTORs demographics in particular because as a Bioware/ME-style game I thought it might show higher numbers of women, but a somewhat decent survey among heavy-involvement players found the female percentage to be around 20%, consistent with previous findings around MMORPGs. http://www.bethanycorcoran.co.uk/2011/09/30/the-old-republic-demographics/