Conservative Supreme Court Justice William Rehnquist, an adamant proponent of states’ rights, surprised everyone when he ruled states had to abide by the Family and Medical Leave Act, prompting some to wonder whether the plight of his recently divorced daughter, a single mom, had influenced his views.

Justice Harry Blackmun penned the Roe v. Wade opinion decriminalizing abortion six years after his daughter got pregnant, dropped out of college and got married. She ultimately had a miscarriage — but did the fact that his daughter’s fate was forever changed by the unplanned pregnancy influence his views? Maybe.

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For better or worse, personal relationships may account for why judges sometimes reach decisions at odds with their political views.

Researchers set out to test the effect of one relationship on judicial decisions: father and daughter. They found that judges who have daughters are more likely to rule in favor of women’s rights than those who don’t.

Maya Sen, a political scientist at the University of Rochester, and Adam Glynn, a government professor at Harvard, looked at 990 cases involving gender issues such as pregnancy discrimination. They evaluated 2,674 votes cast by 244 appeals court judges and found having at least one daughter increased the likelihood a judge ruled in favor of women’s rights in a gender-related case by 7 percent.

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The difference is most pronounced with judges who have one child. If that child is a daughter, researchers found a 16 percent increase in the proportion of cases decided in favor of women’s rights. They found no added impact from having additional daughters.

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Having a daughter made a bigger difference with conservative judges. Having a daughter had a more pronounced effect on judges appointed by Republican presidents, with an average 7 percent increase in the proportion of cases decided “in a feminist direction,” compared with a 4 percent increase for judges appointed by a Democratic president — judges whose decisions were already more likely to be left-leaning.

Previous studies found a link between having daughters and holding more liberal views in the general population. But this is the first study to test that link on judges.

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To see if having daughters affected how judges ruled in cases that weren’t gender related, researchers looked at roughly 3,000 appeals from 1996 to 2002. They found that, in general, daughters didn’t make a difference. They also found that daughters made a difference in gender-related civil cases, not gender-related criminal cases such as rape.

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The study looked at both male and female judges, but there are far fewer female appellate judges, and they are far less likely than male judges to have children. The results were driven mostly by men.

Why do daughters make a difference? “By having at least one daughter,” Sen told the New York Times, “judges learn about what it’s like to be a woman, perhaps a young woman, who might have to deal with issues like equity in terms of pay, university admissions or taking care of children.”