A few years ago, researchers published an eye-opening statistic: 57 percent of parents ages 26 to 31 were having kids outside of marriage. Who were these unwed Millennials and why were they forgoing the traditional structure of American family?

New research from sociologists at Johns Hopkins University and the University of Melbourne has started to answer that question. These aren’t a random assortment of Millennials but disproportionately come from a specific group of young Americans who don’t have college degrees, live in areas with high income inequality, and tend not to have very bright job prospects. The study, published this month in the journal American Sociological Review, found that in areas with the greatest income inequality, young men and women were more likely to have their first child before marriage. The areas with the largest income gaps also tended to have the fewest medium-skilled jobs, which researchers define as jobs that only require a high-school diploma but still enable families to live above the poverty level—jobs such as office clerks and security guards.

The researchers—Andrew Cherlin, David Ribar, and Suzumi Yasutake—analyzed the National Longitudinal Survey of Youth, a federal study of 9,000 men and women who were first interviewed in 1997, when they were 12 to 16, and then interviewed each year through 2011. The data showed that, by 2011, about 53 percent of those women and 41 percent of those men had at least one child. The researchers then separated the parents into three relationship categories: married, living with a partner, or single. They then matched that information to census data on income and employment in the counties where the people lived.

The impact on women was the most dramatic. Young women living in areas with the greatest inequality were 15 to 27 percent less likely to marry before having a child than women in areas with lower inequality. They also found that in areas where men outnumber women, a women is more likely to get married before having a child. The reasoning for this has more to do with money than love. “This is consistent with the idea that when women are in short supply, they can bargain more effectively for marriage or a partnership prior to childbirth,” the authors write.

The study also found a correlation between an area’s high unemployment rates and a greater likelihood that a man would have a child out of wedlock. For both men and women, the larger the availability of medium-skilled jobs, the more likely they were to marry before having their first child. Why exactly, does the economy play a role in marriage decisions? The researchers give this explanation: Men without well-paying jobs are not seen as marriage material. “These men would be less desirable as marriage partners because of their reduced earning potential,” writes Cherlin, a sociology professor at Johns Hopkins and the main author of the study.

He argues that a college degree seems to be a good indicator of the choices millennials will make about getting married or starting a family. His previous research shows that millennials without college degrees are now more likely to have a child without getting married first. Among parents aged 26 to 31 who didn't graduate from college, 74 percent of the mothers and 70 percent of the fathers had at least one child outside of marriage, Cherlin found.

“The lofty place that marriage once held among the markers of adulthood is in serious question among early adults,” he writes.

Both the new study and Cherlin’s earlier work focuses on millennials without college degrees, since they are more likely to have a child by now. This means college-educated millennials were underrepresented in the research. But Cherlin says his research shows the importance of strengthening middle-market jobs and training young adults for them, arguing that doing so would increase family stability.

“We'd have a larger percentage of children born to married couples, who tend to stay together longer than do cohabiting couples,” says Cherlin, via email. “So improving job opportunities for high school graduates, something we'd like to do anyway, would benefit the family lives of young adults and their children.”

In the meantime, it looks like going to college, or at least moving to areas with less inequality, may also improve a person’s chances of getting married before starting a family. And this, Cherlin says, is what most young people still want anyway.