Sometimes it seems that the feminist movement wants to confirm the sexist stereotype that women aren’t very good at complicated math. They repeat simple but misleading statistics about differences in the wages earned by men and women classified as working full time, claiming that the difference is all due to discrimination. For example, Marlo Thomas at the Huffington Post writes today (which, if you didn’t know, is Equal Pay Day):

According to the National Women’s Law Center, the vast majority of American women – working “full-time, year-round” – are still stuck in that shameful 77-cent zone. The gap,says the National Women’s Law Center, translates into “$10,622 less per year in female median earnings.” Those are real dollars that could cover real expenses – like food and school and clothes and health care and childcare.

Yet as I discuss in today’s Wall Street Journal, many other factors affect how much “full-time, year-round” workers make, such as how much time they take off during the year, how many years of experience they have, and the types of occupations they choose. And as Diana Furchtgott-Rothexplains, even the categories of “full-time” and “year-round” contain a lot of variability:

And women do work less than men. The [White House report on the Status of Women] states on page 27 that “women of every educational level and at every age spend fewer weeks in the labor force a year than do men.” In addition, “on the days that they worked, employed married women age 25-54 spent less time in labor market work and work related activities than did employed married men in the same age group-7 hours and 40 minutes, compared to about 8 hours and 50 minutes.”

That’s about 5 hours fewer per week, or, in a 40-hour week, 11 percent. So, just on the basis of hours worked, women should earn 89 percent of what men earn.

Feminists who try to convince women that they earn 77 cents on the dollars for equal work are doing women a disservice. Women are better off understanding that it’s primarily decisions that they make about how much to work and what kinds of jobs to take on that will determine how much they earn.