A new report from the Pew Research Center finds yet more evidence that women are becoming the primary earners in their households. Bryce Covert parses the numbers:

Four in ten mothers are either the sole or primary source of income for their families, a new record, according to a Pew Research Center report released on Wednesday. That figure nearly tripled since 1960.

Yet the trend is not necessarily due to women making more than their husbands. Nearly two-thirds of this group of women workers are single mothers, and just 37 percent are married and have a higher income than their spouses. While the median total family income in houses where mothers earn more than their husbands was nearly $80,000 in 2011, much higher than the national median of $57,100 for families with children, it’s just $23,000 for single mothers’ families – just over a quarter of what families with married breadwinner mothers earn.

Joan C. Williams, meanwhile, looks at the differences in the number of hours men and women work per week:

How many employed American mothers work more than 50 hours a week? Go on, guess. I’ve been asking lots of people that question lately. Most guess around 50 percent. The truth is 9 percent. Nine percent of working moms clock more than 50 hours a week during the key years of career advancement: ages 25 to 44. If we limit the sample to mothers with at least a college degree, the number rises only slightly, to 13.9 percent. …

This “long hours problem,” analyzed so insightfully by Robin Ely and Irene Padavic, is a key reason why the percentage of women in top jobs has stalled at about 14 percent, a number that has barely budged in the past decade. We can’t expect progress when the fast track that leads to top jobs requires a time commitment that excludes most mothers — and by extension, most women.

Previous Dish on female breadwinners here.