Single mothers have been subject to intense scrutiny from pundits, politicians, sociologists, and countless other groups. But in its latest report, the CDC's National Center for Health Statistics sheds light on their male partners instead. And drawing on survey data from thousands of men, it concludes that unmarried fatherhood could be on the decline.

Previous studies show that while the rate of out-of-wedlock births grew over the second half of the 20th century, it started dropping again in the early 21st. Currently, the CDC says that around 40 percent of all births in the US are to unmarried parents. But that doesn't tell us how many fathers are postponing or eschewing marriage, nor does tracking the demographics of single moms alone. "You get a slightly different view of the story than when you just look at women's information," says study author Gladys Martinez. "They do not marry men exactly their age. They do not have children exactly with men of their age."

Instead, the NCHS looked at three decades' worth of records from the National Survey of Family Growth, which tracks things like pregnancy, contraceptive use, and men and women's health. It restricted its search to fathers between 15 and 44 years old and only looked at their first child, something Martinez says was done in order to eliminate extra variables like birth order. From 1980 to 1989, 42 percent of the fathers hadn't married when their first child was born. That number went down only slightly in the '90s, but over the next decade, it dipped to 36 percent.

Unmarried fathers are more likely to be living with a partner "For women, we see that there's been a decline in the rate of non-marital childbearing, so [the numbers are] kind of comparable," says Martinez. That decline, though, is fairly recent — it peaked around 2008. "I was actually very surprised," says Lenna Nepomnyaschy, an associate professor who works on family policy at Rutgers and was not involved in this study. "Given the national figures for the proportion of all births that are to non-married mothers — those have been going up over the last three decades." Both she and Martinez agree that it's difficult to draw direct comparisons with other studies, though. They might address the same questions, but they're looking at different kinds of data, especially because it only counts first births.

It does reflect one major change that other studies have found: a slowly growing number of parents are choosing to live together without marrying. When people think of unmarried parents, "they assume that most of that is the mother by herself," says Martinez. "Looking at the increases at cohabitation, that shows you that that's not really true." Nineteen percent of unwed fathers were living with their partners in the '80s, compared to 24 percent in the '00s. They're also getting older. Where less than a 10th of unmarried fathers (not fathers in general) were 25 or older at the start of the study, they now make up a third of the group. Martinez cautions that this could be the result of an aging population, not a fundamental change in how people think about marriage or reproduction, but more research would be required.

The survey found significant differences in race and ethnicity. For all three decades, over half of black and Hispanic fathers were unmarried, compared to between a third and a quarter of white ones. While the percentage of unmarried black fathers is still highest, though, it's actually dropped significantly, from 77 percent in the '80s to 66 percent by the '00s.

Understanding the roots of these changes is the next step It will take more work to figure out what's caused these changes, but ultimately, Martinez hopes this study will help improve the lives of these fathers' children — other research suggests that whatever the cause, children born to unmarried parents can have a higher risk of health problems, at least in the US. "There is no reason that children being raised by cohabiting parents should be any worse off than children being raised by married parents," says Nepomnyaschy, pointing to countries in Europe with extremely low marriage rates. "The problem is that in the US, people who cohabit instead of getting married tend to be lower-educated, tend to have lower incomes, and those relationships tend to be less stable." This increases financial pressure and, if the relationship breaks up, could leave one parent — usually the mother, even with single-father households getting more common — trying to take care of a child without support.

Policies that promote paid parental leave, access to child care and health care, and access to higher education could all help alleviate these pressures, but they won't necessarily increase fathers' involvement. "Few of the responsible fatherhood programs have made much of a difference," says Nepomnyaschy. "It would be important to understand whether broad economic and social policies (that are not specifically aimed at fathers) might have more impact on getting men to get married or getting fathers to be more involved with their children." This could include reforming the prison system and helping reintegrate men coming out of it, or increasing the minimum wage overall. Even if the final policies don't focus directly on fathers, though, this survey is a step toward figuring out what works.