Illustration by Barry Falls

Parents of girls are 5 percent more likely to divorce than parents of boys. Economists first analyzed the data that way in 2003, when Gordon Dahl at the University of Rochester and Enrico Moretti at U.C.L.A., identified that gap, and noted that it widened as you added boys or girls to a family. Parents of three girls, for instance, are 10 percent more likely to split than are parents of three boys. And, they found, an unmarried couple is more likely to marry if they learn their unborn child will be a boy than a girl.

For years the interpretation of that data has been that boys are an asset to a marriage and girls are somehow a liability. (One example of this line of thought is from Steven Landsburg, also of the University of Rochester, who laid out his families-prefer-boys argument in Slate back when the study was first published, and also in a chapter of his book “More Sex Is Safer Sex.”) Maybe fathers prefer boys and will work harder at keeping a relationship intact in order to raise them? Or the quality of married life is better with boys? Or boys are more likely to fall apart when their father leaves — hence their father doesn’t? However the question was phrased, it was basically about the benefits of boys.

But on the Web site of Psychology Today, Anita Kelly, a professor of psychology at Notre Dame, speculates that perhaps the opposite is true: that women who have daughters have less need for a husband. After all, she says, nearly three-quarters of all divorces involve a wife leaving her husband, so the question is not why do men stay for boys, but rather why mothers of daughters are divorcing more than mothers of sons.

Noting other studies, which show that adult sons who live at home increase the “chore” burden on their parents while adult daughters decrease it, and also that “females offer more and better social support than men,” she concludes:

… wives with daughters are less likely to stay with their husbands because they know that with a girl, they’ll never be lonely or without help. Thus, they may be less willing to tolerate any bad behaviors from their husbands (and less willing to stay married) because they don’t need their husbands as much. This idea could even explain why couples expecting a girl are less likely to marry: A woman carrying a girl anticipates that she won’t need a husband.

What do you make of the data? Does the idea that a girl will fill an emotional void influence whether a mother stays or leaves? If not, how to explain the statistical gap?