Today is "Equal Pay Day," an annual symbolic protest of the supposed gender gap in wages. It is based on the number of additional days that women have to work into the new year to equal the median wage of men in the prior year. Last year the median annual income of women working full time and year round was 77% of men's median income. Thus, women need to work an extra quarter of a year - that is, until today - to catch up.
The implication of this argument is that women make 77% of what men make due to discrimination. A moment's thought, though, should dispose of this argument. If women really did exactly the same work as men for only three quarters of the cost, no rational employer would hire men at all.
The American Association of University Women, who calculated this ratio, admit that when you control for several things that should be controlled for - college major, occupation, industry, sector, hours worked, workplace flexibility, experience, educational attainment, enrollment status, GPA, institution selectivity, age, race/ethnicity, region, marital status, and number of children - the gap drops to 5% one year after college graduation.
The biggest difference is not simply between men and women, but between fathers and mothers. Married fathers are likely to work more, more steadily, and seek every opportunity to make more money for their families. Married mothers are more likely to scale back their work to have a better balance with their family life. Married couples usually divide labor and specialize for the good of the family as a whole.
Of course there is some sex discrimination in employment. The Lilly Ledbetter Fair Pay Act, signed into law by President Obama a few years ago, did address a real problem.
But most of the gender gap in wages is due to different choices of how to live that men and women, and especially fathers and mothers, make about work and family life.