01/31/2014 05:40 pm ET Updated Feb 03, 2014

Marrying Someone Just Like You Is Bad For The Economy, Say Economists

Marrying someone with similar interests and background is often touted as the recipe for a great marriage -- but a new study suggests that our tendency to choose partners just like us could be to blame for the growing income gap in America.

University of Pennsylvania professor Jeremy Greenwood and a team of economists analyzed marriage patterns from 1960 to 2005 and compared them to income distribution in those same years. The data, taken from U.S. Census records, revealed that people's tendency to marry others with their same education level -- which they call "assortative mating" -- has increased in the last few decades. Accordingly, wealth in America has been distributed unevenly; through marriage, the rich get richer and the poor get poorer.

How did they come to this conclusion?

The researchers calculated the income inequality in both 1960 and 2005 using the Gini coefficient -- a number between zero and one in which zero means no inequality and one means that one person holds all the wealth. They determined that if "assortative mating" did not occur -- meaning Americans did not pick partners based on education level and instead chose at random -- the distribution of wealth in America would be better. Here's what they found:

Income inequality in 1960 was determined to be 0.34. Economists then took the 1960 data and calculated what the Gini coefficient would have been if people had chosen random partners rather than those who were similar to them. That new number was 0.33 -- relatively the same.

Income inequality in 2005 was calculated to be 0.43 -- a higher level of inequality. This time, when economists applied random mating to the data, the coefficient dropped to 0.34.

In other words, the tendency to choose a spouse from the same educational level -- which, in turn, is linked to higher income -- has caused the distribution of wealth to polarize more so than if we married outside our circles.

Researchers hypothesized that one reason "assortative mating" is having such a profound effect on income inequality is because more married women are joining the work force. In 1960, 42 percent of women aged 25 to 54 worked outside the home. Today, that number is at 75 percent, according to Bureau of Labor Statistics.

"If mating was completely random, then having women working would tend to equalize income across families," Greenwood told U.S. News and World Report. "Statistically speaking, say if you had a high-earning man he'd be offset by a low-earning woman" and vice versa.

But because mating isn't random, educated men and women's combined earnings put them in a higher income bracket -- contributing to the income gap.

Click here to read the full paper.

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