Hi Leah - for starters, here's a blog I wrote on the topic in 2011:
http://www.bookbrowse.com/blogs/editor/index.cfm/2011/2/11/Why-literary-mags-review-three-times-more-male-writers-than-female
I attended a forum last year, 2013, at the National Book Critcs Circle annual meeting which discussed the topic. The long and short was that most of the literary magazines had not changed their ratios significantly in the intervening two years, but there was one exception and that was Tin House Quarterly. The editor of Tin House was part of the panel. He said that he had taken to heart the results of the 2011 survey and changed his processes in order to ensure that he gave approximately equal coveage to men and women.
But, and this is an important but, to achieve this ratio he was having to actively follow up with women writers to encourage them to submit. To the best of my recollection, the long and the short of what he said was that if he politely declined a piece of work by the average male writer the writer would bounce back with a new submission within a few weeks; but if he did the same to the average female writer he would never hear from her again - even if he had made it clear that he was declining not because of the quality of the work but simply because it didn't fit in the context. In other words, his view was that the fault does not lie entirely with the literary mags but with women writers for not pushing themselves forwards as much as men do. To compensate for this he had made the conscious decision, and was investing the time, to actively reach out to women writers to encourage them to submit.