"Even feminist Hanna Rosin dismissed this metric last August, also concluding that the actual difference is (a) much smaller, and (b) due to “rational choices” made by women:
The official Bureau of Labor Department statistics show that the median earnings of full-time female workers is 77 percent of the median earnings of full-time male workers. But that is very different than “77 cents on the dollar for doing the same work as men.” The latter gives the impression that a man and a woman standing next to each other doing the same job for the same number of hours get paid different salaries. That’s not at all the case. “Full time” officially means 35 hours, but men work more hours than women. That’s the first problem: We could be comparing men working 40 hours to women working 35. …
Economists Francine Blau and Lawrence Kahn did that in a recent paper, “The Gender Pay Gap.”.”They first accounted for education and experience. That didn’t shift the gap very much, because women generally have at least as much and usually more education than men, and since the 1980s they have been gaining the experience. The fact that men are more likely to be in unions and have their salaries protected accounts for about 4 percent of the gap. The big differences are in occupation and industry. Women congregate in different professions than men do, and the largely male professions tend to be higher-paying. If you account for those differences, and then compare a woman and a man doing the same job, the pay gap narrows to 91 percent. So, you could accurately say in that Obama ad that, “women get paid 91 cents on the dollar for doing the same work as men.”
The point here is not that there is no wage inequality. But by focusing our outrage into a tidy, misleading statistic we’ve missed the actual challenges. It would in fact be much simpler if the problem were rank sexism and all you had to do was enlighten the nation’s bosses or throw the Equal Pay Act at them. But the 91 percent statistic suggests a much more complicated set of problems. Is it that women are choosing lower-paying professions or that our country values women’s professions less? And why do women work fewer hours? Is this all discrimination or, as economist Claudia Goldin likes to say, also a result of “rational choices” women make about how they want to conduct their lives."