Because marriage can offer a more stable and healthier environment in which to raise children, this is bad news for girls, says Shelly Lundberg, an economics professor at the University of Washington and co-author of the study.
"The size of this effect was dismaying," she says. "In the U.S. we believe there is no gender discrimination, and there is no stark discrimination against women. But there are dimensions, especially in the father's behavior, in the way the household spends its money and time and in the stability of the family where boys versus girls matters."
At a time of high divorce rates and a large number of out-of-wedlock births, finding ways to promote more stable families is very important, she says.
"This is a huge policy issue," Lundberg adds. "What does it take to preserve the family? What is it that helps to promote stable, healthy families? Our hope is that our work will help us develop an understanding of what forces encourage family formation and father involvement with children."
The results of the study, financed in part by the National Science Foundation, appear in the May issue of Demography.
For the study, which looked at how a child's gender affects family formation, especially after a premarital birth, Lundberg and her university colleague, associate economics professor Elaina Rose, used data from the national Panel Study of Income Dynamics to identify a sampling of 600 children born to single mothers from 1969 to 1993. Of those, 51.7 percent were boys, which is in line with biological expectation, Lundberg says.
When looking at the marital patterns for the mothers of those children, the researchers found the effect of gender on the rate of marriage to biological fathers was very large. The only other significant factors affecting marriages were that white women had a higher rate of marriage compared to other ethnic groups and that first-time mothers married at a higher rate than mothers with more than one child.
The mothers of 21.6 percent of the boys married the child's father, compared to only 15.2 percent of the mothers of girls, which translates statistically into a 42 percent higher rate of the mothers of sons eventually marrying the father than of mothers of daughters marrying the father, Lundberg says.
The reasons for these effects could be several, Lundberg says.
"There could be dynastic considerations for the man, or the thought that a man would be more useful to a boy and have more fun," she says. "Or a mother of a son might feel it's more important for there to be a father in the household, and will perhaps settle for less. We can't tell."
"It's concerning that there is such a dramatic sex difference," says Nadine Kaslow, a professor of psychiatry and behavioral sciences at Emory University School of Medicine in Atlanta. "The upside is that women who have sons have a pretty good chance of getting a man in the picture and providing two parents in the home, but the depressing part of the study is what this means for girls and for single mothers with female children."
Overall, including marriages to both biological fathers and to men who would be stepfathers, 56.8 percent of the single mothers of boys married, compared to 51 percent of the mothers with daughters, which translates statistically into an 11 percent higher rate of marriage for the women with sons.
This study is a continuation the work that Lundberg and Rose are doing to better understand what makes families stable in the face of today's high rates of divorce and premarital births.
Their previous studies, for instance, have found that fathers work about 40 hours a year more after the birth of a son than a daughter and their hourly earnings are higher if they have sons rather than daughters. Work by other researchers has also found fathers are more involved in their families' lives if they have sons rather than daughters.
This report from the Alan Guttmacher Institute discusses the relationship between premarital births and marriage. Detroit is the city with the highest number of premarital births, according to the Detroit News.