Why do women initiate more domestic violence than men?

When domestic violence escalates, women often end up more battered, so knowing this why are they much more likely than men to initiate domestic violence?
Update: "Women More Likely to Commit Domestic Violence, Studies Show" http://www.thenewamerican.com/usnews/crime/item/19133-women-more-likely-to-commit-domestic-violence-studies-show "Harvard study says 70 percent of domestic violence is committed by women against... show more "Women More Likely to Commit Domestic Violence, Studies Show"
http://www.thenewamerican.com/usnews/crime/item/19133-women-more-likely-to-commit-domestic-violence-studies-show

"Harvard study says 70 percent of domestic violence is committed by women against men"
http://newscastmedia.com/domestic-violence.htm
Update 2: Yet more than 200 studies have found that women initiate at least as much violence against their male partners as vice versa.
http://www.washingtontimes.com/news/2009/jul/14/a-domestic-violence-victim/#ixzz3gjCuQxbG
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