From last year....

"Once education, marital status and occupations are considered, the 'gender wage gap' all but disappears.
"

As President Obama said in the State of the Union address, women "still make 77 cents for every dollar a man earns," a claim echoed by the National Committee on Pay Equity, the American Association of University Women and other progressive groups.

The 23% gap implies that women work an extra 68 days to earn the same pay as a man. Mr. Obama advocates allowing women to sue for wage discrimination, with employers bearing the burden of proving they did not discriminate. But the numbers bandied about to make the claim of widespread discrimination are fundamentally misleading and economically illogical.

In its annual report, "Highlights of Women's Earnings in 2012," the Bureau of Labor Statistics states that "In 2012, women who were full-time wage and salary workers had median usual weekly earnings of $691. On average in 2012, women made about 81% of the median earnings of male full-time wage and salary workers ($854)." Give or take a few percentage points, the BLS appears to support the president's claim.

But every "full-time" worker, as the BLS notes, is not the same: Men were almost twice as likely as women to work more than 40 hours a week, and women almost twice as likely to work only 35 to 39 hours per week. Once that is taken into consideration, the pay gap begins to shrink. Women who worked a 40-hour week earned 88% of male earnings.

Then there is the issue of marriage and children. The BLS reports that single women who have never married earned 96% of men's earnings in 2012."

[B]"The supposed pay gap appears when marriage and children enter the picture. Child care takes mothers out of the labor market, so when they return they have less work experience than similarly-aged males. Many working mothers seek jobs that provide greater flexibility, such as telecommuting or flexible hours. Not all jobs can be flexible, and all other
things being equal, those which are will pay less than those that do not."[/B

Mark J. Perry and Andrew G. Biggs: The '77 Cents on the Dollar' Myth About Women's Pay - WSJ