April 17 is Equal Pay Day in the U.S commemorating the 49th anniversary of the Equal Pay Act legislated by JFK in 1963. Typically - even today - feminists (and even President Obama) trot out the false stat that women are being discriminated against because they are paid less than men - using the "77c per $1" that Men make - which is a lie. Kim Hymowitz of the Manhattan Institute has covered the topic extensively and after adjusting for hours worked (on the reasonable assumption that if you work more you get paid more) one removes about 10% of the difference. When one adjusts for other factors that may lead to observable wage differences - parental status, experience, college major and industry - the gap falls to 7%. This could be related to women having children and the fact women work fewer hours, choose less demanding jobs so they can parent their kids. In fact a number of researchers have found that if you consider only childless women, the wage gap disappears.
A similar Canadian Study from the other side can be found here and it shows 5-15% gap - all explainable by variances in others factors like risk and specialty.