Marriage could serve as an equalizer. Higher-earning, working women could easily make up for the losses of their middle-income husbands. Pigs could also fly. Today, marriage actually makes income more unequal across households. One reason is that marriage itself has become more unequal. Forty years ago, lower-earning Americans were more likely to be married than higher-earning ones. No more. Individuals who are married are more likely than ever to be highly educated and thus high-income already. But, a second reason exists for marriage not serving as an equalizer: “assortative mating.”

Now, before you delete your browsing history and hide the laptop from the kids, assortative mating isn’t quite as exciting as it sounds. I mean…I think it’s exciting. But, I’m admittedly kind of boring. In any case, assortative mating refers to the fact that people are increasingly marrying other individuals with the same level of education. Before looking at some illustrative data, a logical question is: why is this happening?

Why Would Assortative Mating Rise?

To understand the rise in assortative mating, it’s easier to think of the choice of a spouse from a male’s prospective. (OK, it’s just easier for me to think of it from a male’s perspective, because I am a man.  If I were a better writer, I could probably write from multiple perspectives.) In 1975, the man’s choice might hinge on a variety of factors. For example, how capable was a potential match with housework? Or, how good would she be with kids? Or, how attractive was she? Today, many of those same things would get you a smack upside head.

The point is, one thing that might not have been on the spousal checklist was the woman’s earnings potential.  Once married, a woman was unlikely to work very much. And if she did, she wouldn’t make much anyway. Today, a man deciding to marry would be wise to consider the future earnings of his spouse.  If he can choose a woman who will contribute to the household finances, he will be better off.  Today, if a college-educated male can marry a college-educated female, their household will have considerable earnings power.

The result is that, in the past, there would have been little relationship between husband and wive’s education. Today, one expects the existence of “power couples” with two high-earners becoming more and more common.  This increasing relationship between husband’s and wife’s education is the notion of “assortative mating.”  But while that all sounds plausible in theory, do we see it in the data?

Assortative Mating: Taking it to the Data

Looking in the data for an increase in assortative mating is a little difficult.  While a logical approach would be to see if we have a lot more couples with two college-educated people, this would miss the point.  After all, you have seen that the share of women with a college degree has gone up a lot. So, naturally, we will have more couples with two college degrees than in the past.  This fact would not reflect an increase in assortative mating, but simply the fact that both men (and especially) women are more educated.

Instead, we can look at what share of couples actually has two college-educated people versus what would have happened if people married randomly. What would the share of couples with two college degrees be if people married randomly?  What is the actual share? If the second number is higher than the first, it would imply people are not getting married randomly and high-educated people tend to marry other highly-educated people.

Figure 1 shows the results of this exercise. The solid line (actual) being higher than the dashed line (random) means assortative mating has always been around. If people randomly married in the seventies, only 2.8 percent of marriages would have had two college-educated people. Instead 8.7 percent of marriages included two college-educated people.  The figure also shows that the pattern has been exaggerated with time.  Today, we would expect to see about 15.8 percent of married couples consisting of two people with a bachelor’s degree or more.  Instead, we see 31.4 percent of couples in this situation. So, what does this have to do with income inequality?

Figure 1. Actual Share of Couples with Two College-earners Versus if Marriage was Random, 1975 to 2019

The Rise of Power Couples

To bring the discussion back to household income inequality, I want to define a “power couple” as a couple where both people are: 1) earning money; and 2) have a bachelor’s degree or more.  The question is: have these couples become much more prevalent among those at the top, driving the income inequality we saw a few weeks ago?

Yup (believe it or not, “yup” is a technical economics term). Figure 2 shows that, back in the mid-1970s, these couples were not that prevalent at any earnings level.  This fact makes sense; women seldom were college educated and seldom worked. So, power couples were rare even at high-income levels.  The figure also shows that these couples are still relatively rare in the middle and bottom of the income distribution. However, they are now very common at the top. Over a third of high-income married households and nearly half very high-earning married households consist of two college-educated earners.

Figure 2. Share of Married Households with Two College-educated Earners by Earnings Percentile

Conclusion

The last two posts have made two things clear. First, marriage itself is becoming more unequal. And, for those who do get married, increasingly like is marrying like. These two facts mean that marriage is not the great equalizer it could be. Instead, marriage is something that, like many other trends, is tending to make inequality even worse. Next week, I will get to some solutions — things that might make marriage an equalizer. But, what you should realize already, is that the trends that are hurting middle-income workers play a major role — and those things are hard to fix. For now, just know that assortative mating is on the rise, and with it inequality.