Here is a link to an exhaustive, and frankly, too long dissertation on the disparity of the application of the death penalty based upon gender.
Basically it boils down to men are 7 times as likely to be executed as women for the same crimes.
Overall, only about 1.5% of convicted murderers are executed (and those are mainly in Texas and Florida).The idea that the death penalty is a deterrent or fair is obviously nonsense since the only way someone gets executed is when the case becomes a media circus and the defense is incompetent.
It's cultural.
Western people value women more than some cultures, so fewer women are put on death row. Contrast that with a Middle Eastern country or India where women are looked down upon and the gender noticeably flips.
I heard in China it's pretty even but here in Japan I've never heard of a woman being executed.
To the death penalty being a deterrent, I'd go back to literature at the turn of the last century and before. Even in films from the 30's people are afraid of The Chair. Go back further to the UK and they were brutal about the death penalty. There's a three-part tv miniseries (I haven't gotten around to watching) called Gunsmoke that shows the death penalty as a part of daily life, a kind of spectacle. The further we remove death from the public view the more abstract it becomes and the less impact it likely has.
