A man places an engagement ring on his new fiance's hand after she says yes to marriage.

Is Marriage Responsible for Economic Inequality?

According to one study, how we choose our spouses has boosted inequality substantially. 

A man places an engagement ring on his new fiance's hand after she says yes to marriage.

According to one study, choosing spouses within the same income bracket has boosts inequality substantially. 

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If you really want to fight inequality you could campaign for a higher minimum wage or advocate for education reform. Or, as it turns out, you could do your patriotic duty and marry down (or up).

According to a new study, the way Americans choose their spouses has contributed significantly to increased inequality. From 1960 through 2005, Americans increasingly engaged in "assortative mating" – an academic way of saying rich people are increasingly marrying rich people, and likewise poor people choose poor spouses.

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The study focuses on one measure of inequality called the Gini Index. The index measures a society's inequality on a scale of 0 to 1, where a measure of zero means all income is perfectly equally distributed, and a measure of 1 means only one person has all of the income. In 2005, the Gini coefficient was 0.43, according to the study, but if people had chosen their spouses at random (rather than picking fellow aristocrats or paupers) it would have been 0.34. Meanwhile, in 1960, the Gini index was 0.34. When the study's authors conducted a model in which those people chose their spouses at random, the figure barely moved, registering a 0.33.

Not only that, but if people in 2005 chose their mates in the same way that 1960s couples did, there would be "a significant reduction in income inequality," from 0.43 to 0.35, the authors write. In other words, people are seeking out similar people to marry more so now than in 1960, and it has helped to push inequality upward.

One key factor in this shift is the growing share of women in the workforce – in 1960, only around 38 percent of women participated in the labor force. As of 2005, it was around 59 percent. More women are earning money, and they also have increasingly earned college degrees, which has made for higher and higher salaries. If people chose spouses at random, this would not have affected inequality. However, that's not how things work, says one of the studies authors.

"If, when more women work, if mating was completely random, then having women working would tend to equalize income across families. If you just matched in a random manner then statistically speaking say if you had a high-earning man he'd be offset by a low-earning woman," and vice versa, says Jeremy Greenwood, professor of economics at the University of Pennsylvania.

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The differences between choosing a like partner or not can be dramatic. According to the study, in 2005 if a woman with education beyond college married a man with less than a high school degree, their combined income would have been around 92 percent of the average household income nationwide. But if that same woman married a man of the same education level, their income would have been 219 percent of the average household income.

This is not to say, however, that other factors are not at play. The same study shows that in 1960, a married man and woman, both of whom had less than a high school diploma, would have earned around 77 percent of the average household income, while in 2005, they would have earned around 41 percent. Meanwhile, a couple in which both partners had post-college credentials in 1960 would have earned 176 percent of the mean, while in 2005 that share would have been 219 percent. (Interestingly, the share barely moved for college-graduate couples, from nearly 153 percent to 160 percent.)

While more and more women have been earning more and more money, spouses have also been increasingly choosing people of their own income levels. Why is everyone increasingly marrying in their own income pools? Greenwood has a theory, and it has to do with the household division of labor.

In the past, he says, "I think how good a woman was at managing the home and how good a male was in bringing in an income were probably the top considerations. When we moved to modern times a woman's value at housekeeping is probably much lower than it was historically."

Earlier in the 20th century, meanwhile, before the widespread use of machines like microwaves and washing machines, "looking after the home was such a labor-intensive activity," says Greenwood.

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Less household labor combined with more women working outside the house has meant that men and women are choosing their partners on different merits, and women's earning power may be playing a greater part in the equation than it once did (likewise, men's earning power may be playing less of a part). Or it may have less to do with money – people can simply now be "pickier" about their spouses, says Greenwood. That may mean seeking out a spouse with whom one shares common interests and values – seeking someone of similar class or education levels can sometimes go a long way in fulfilling those commonalities.

All of which may make for a fascinating irony: more gender equality may have led to greater economic inequality. So when President Barack Obama both champions working women and lambasts inequality, as he did in his State of the Union address, he may want to add one more directive: single Americans, expand your dating pools.

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