OF THE many glass ceilings constraining women's careers, one is particularly important yet often overlooked: the wage of the husband. In a new paper, Marianne Bertrand, Emir Kamenica (both University of Chicago) and Jessica Pan (National University of Singapore) show how thick this ceiling really is.

In a country like America, in which men on average earn more than women, it follows almost naturally that the wife often earns less. However, the pattern of relative income of men and women at young(ish) ages in a marriage is striking: there are many young couples in which the wife earns slightly less than her husband, or just as much, but far fewer as relative income reverses, that is, when the wife earns more. And this pattern is not driven by older couples; the researcher only use couples around the time of first marriage (22-34) for this part of the study. Despite some progress in recent decades, the social norm "men should earn more than their wives" seems to be alive and well.

That is not only a curious fact; it has consequences, too. The researchers show that women with the potential to earn more than their husbands quit their job altogether more often than otherwise similar women in comparable families. If they do work, they use their earnings potential to a lower degree. That's bad news for the economy.

The paper offers some hints as to why women who could outearn their husbands choose not to work at all, or to work less. For instance, norms affect the division of household chores, but economically in the wrong direction. If a husband earns less than his wife, she might rightfully expect him to take on some additional responsibilities at home. In reality, however, if she earns more, she spends more time taking care of the household and their children than otherwise similar women in comparable families, who earn less than the husband. One wonders whether such women feel compelled to soothe their husbands' unease at earning less.

For the couples themselves, the dynamic may be a problem. As long as the woman earns less, her income does not cause trouble in the marriage. Once she earns more, however, marriage difficulties jump and divorce rates increase. Interestingly, it does not seem to matter whether she earns only slightly more, or substantially more—an indication that it is not female income per se, but the mere fact of earning more, that causes trouble.

Economists may wonder why people with "rational expectations" enter such a marriage at all. The answer is: many do not. The marriage market, as economists bluntly call it, clears much less often in regions in which more women have the potential to outearn men, the paper shows.

The authors are careful not to overstate their conclusions. But even if some of these results are merely descriptive, they point towards a tricky future for the gender pay gap and for an economy that can hardly afford to waste female potential. Norms are stubborn things. Changing norms requires a long breath, and potentially the support of targeted policies. One such policy could be a parental leave exclusively for fathers (as in Sweden and recently in Germany), to shift focus away from the male bread-winner model. But even these policies take long to change norms. The marital glass ceiling may prove the hardest to break yet.

* Marianne Bertrand, Emir Kamenica and Jessica Pan (2012), “Gender identity and relative income within households”, forthcoming

Correction: This article initially said that the number of couples in which earnings between partners are roughly equal drops rapidly with age. In fact, couples in which men outearn women are much more common at all ages.