It's no surprise that households have changed in the United States in recent decades. As marriage rates have declined, only 63 percent of children in the U.S. are now raised in homes with married parents. That number is even lower among the children of parents who don’t have a four-year college degree, one economist says.

But bringing awareness to the advantages of married families has become an "ideological battle," University of Maryland economics professor Melissa Kearney told Fox News Digital. 

In her new book, "The Two-Parent Privilege," she analyzed research from dozens of economists, sociologists and psychologists on the class gap, and found married parents to be a common denominator affecting a child's success.

Married parents tend to have more time, energy, and resources available to bring to their children, she said. Children who are raised by parents who are in a stable, long-term relationship are more likely to graduate high school, to graduate college, and to have higher earnings as adults. The opposite is true for children who don't grow up in these households.

A GOOD MARRIAGE IS THE ‘NUMBER ONE PREDICTOR OF HAPPINESS’ FOR MEN AND WOMEN, SOCIOLOGIST SAYS

"So kids who grow up in a one-parent household are more likely to grow up in poverty. They're less likely to finish high school, they're less likely to go to college, they're more likely to get suspended from school or be involved with the criminal justice system," Kearney said. 

This has less to do with parenting styles and more to do with the constraint on household resources, parental time, and supervision available to just one parent, she clarified.

While this information shouldn't be controversial, Kearney says just talking about the benefits married parents bring to children has unfortunately become politicized.

"And I think this is part of the problem as to why I don't think we do more to really focus on efforts to strengthen families and two-parent families, because it has become a very politicized issue. One of the main things I'm hoping to accomplish with my book is to take this out of the ideological cultural wars and say that, look, as a matter of social science, it's clear that kids benefit when they are growing up in healthy, stable two-parent homes," Kearney said.

FEMINIST JOURNALIST: BLAME ‘CONSERVATIVE POLICIES’ FOR DECLINE OF MARRIED PARENTS

She hopes her book will prompt a cultural discussion in how society can change these trends, at the policy level and elsewhere.

"We should talk about and experiment with and fund programs to try and figure out how to help more adults who have a child together, achieve that family structure for their kids and for themselves. We should be doing that at the same time as we're trying to strengthen the safety net in productive ways and improve schools," Kearney said. "It shouldn't be an ideological battle."

According to a report from the AEI-Brookings Working Group on Childhood in the United States, the percentage of young children, 12 and under, living in households with married parents, "declined from 83 percent in the mid-1970s to 71 percent in 2019." 

"This decline in children living with two parents was accompanied by a steady increase in the percentage of children living with only their mother. This trend was entirely driven by a rise in the share of children living with never-married mothers, which increased from 3 percent in 1976 to 18 percent in 2019. The share of children living with divorced mothers held relatively steady over this period at 6 percent," the report said.

Nearly half of adults in a new Pew Research Center poll, believe the trend of children being raised by unmarried parents will have a negative impact on the country's future.

While on average, across all groups, kids from married parent homes have better outcomes, Kearney says there are clear outliers to these findings. For instance, children who are raised by two parents without college degrees may fare worse than children raised by a single mother with a college degree, she said. When a parent who has been convicted of a crime is removed from the home, kids typically fare better with just one parent, she explained.

There is no clear "policy lever to pull" to change these trends, Kearney says. Although she supports a strong Medicaid program for low-income children and an expanded child tax credit, she thinks there should be more funding and research into developing programs promoting safe and stable families as well.

"I agree that we need more public support to economically insecure families, but a government check is never going to make up for all the income and other types of support a loving, working second parent in the home would bring. Even in countries with much more generous welfare states than the U.S., family background matters for children’s outcomes. We should have a stronger safety net in the U.S., but we should also invest directly in parents and their ability to establish strong families." Kearney wrote.

Marriage doesn't just impact children's happiness; it also is the "number one predictor of happiness in America today," according to sociologist Brad Wilcox. 

"What we see in the research is that both men and women who are married are almost twice as likely to be happy compared to their fellow Americans who are not married," he previously told FOX News Digital.

The 2022 General Social Survey found 40% of married mothers between the ages of 18 and 55 report being "very happy" with their lives, while only 22% of unmarried women with no children and 17% of single mothers, report the same. Wilcox's organization notes the low rates of happiness reported by single mothers parallel similar findings in 2020 and 2021. 

Married men were also "about twice as likely to be very happy compared to their unmarried peers," the Institute for Family Studies says. Like single mothers, single fathers were the least likely to report being "very happy" with their lives, according to the same study.

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