The classical economic explanation for the decline of marriage among the low-income starts by blaming the guys. Sorry, guys. This theory of marriage starts with "gains from trade" (a wonky term for "what each side brings to the table"). You'll note that declining marriage rates correlate roughly with declining male earnings (see graph below, also from the Hamilton Project). Men simply offer less financial security than they used to -- especially compared with women, who are more financially self-sufficient than ever.

This classic approach to marriage economics might explain why there are fewer overall marriages. But it fails to explain something that might be even more interesting: Why there are so very few marriages where women earn more than their husbands, and why such marriages are so troubled.

This story is best told through pictures. Here's the distribution of marriages by the wife's share of household income. As you can see, there's a sharp drop-off after the .5 mark, where the women earns more than 50 percent of the household income. That means it's surprisingly rare to see a woman earn 60 percent or more of a couple's income today, even though women earn a similar share of all today's bachelor degrees.



This drop-off is simply too steep to be explained by randomness or classical economics. If men and women were forming marriages without concern for relative incomes, we'd expect a smoother distribution curve, more like this guy ...



If classical economics doesn't do the trick, maybe it's because the dearth of female breadwinners has little to do with classical economics. In a cool new paper, Marianne Bertrand, Jessica Pan, and Emir Kamenica pose a theory that some people might find controversial but others might find intuitive: What if there's a deficit of marriages where the wife is the top earner because -- to put things bluntly -- husbands hate being out-earned by their wives, and wives hate living with husbands who resent them?

If this were true, we would expect to see at least three four other things to be true. First, we'd expect marriages with female breadwinners to be surprisingly rare. Second, we'd expect them to produce unhappier marriages. Third, we might expect these women to cut back on hours, do more household, or make other gestures to make their husbands feel better. Fourth, we'd expect these marriages to end more in divorce. Lo and behold (as you no doubt guessed), the economists found all of those assumptions borne out by the evidence.

"There simply aren't nearly as many relationships with women out-earning men as we would expect [through random pairing]," Kamenica told me. "And women who should out-earn their husbands based on their education and other demographics are more likely to stay at home [and not work] than the similar women who don't out-earn the husbands," Kamenica said.

