Her core facts are these:
- 37.7% of wives with any earnings at all make more than their husbands (2009, Bureau of Labor Statistics).
- Women now hold 51% of managerial and professional jobs.
- Women are better represented in 9 of the 10 job categories most likely to grow in the next decade.
Mundy does outrun her data a bit. The recent rise from 20-something percent of wives outearning their husbands to 30-something percent may be a temporary effect of the "mancession" of 2008 - 09, in which men disproportionately lost their jobs. And "nearly 40%" is not the same as "the new majority," as her subtitle claims.
Moreover, women who make only a little more than their husbands are not quite what we usually mean by "breadwinners" (and of the course same is true with the sexes reversed).
Mundy's best observation is that women having been doing better than men in school for a generation, which comes just at the time when our economy is increasingly knowledge-based. This should give the average woman a growing advantage in both actual knowledge and in credentials over the average man.
I think the main phenomenon that Mundy's facts reveal is that as wives match or better their husbands' educational credentials and career aspirations, their earnings are more equal. Usually he earns a bit more, sometimes she does. This means that in many couples, neither is really the breadwinner, but together they support their family in roughly equal measure.