DETROIT — The author of a controversial study of adult children often cited by opponents of gay marriage defended his work in court Monday but also said it’s too early for social scientists to make far-reaching conclusions about families headed by same-sex couples.
University of Texas sociologist Mark Regnerus testified for more than three hours as a witness for the state of Michigan, which is defending a ban on gay marriage. The constitutional amendment, approved by voters in 2004, is being challenged by two Detroit-area nurses in a rare trial.
Regnerus was the leader of a study that screened thousands of people, ages 18 to 39, and found roughly 250 who said they grew up in a house where a parent eventually had a same-sex relationship.
He found they were more likely to have problems — welfare dependence, less education, marijuana use — than young adults from stable families led by heterosexuals. He later acknowledged that his study didn’t include children raised by same-sex couples in a stable relationship.
The results ignited a blast of criticism when they were published in an academic journal in 2012.
‘‘Severe and swift,’’ Regnerus told US District Judge Bernard Friedman about the response.
Regnerus also said the university opened an investigation about possible scientific misconduct but closed it early in the process.
University of Texas sociologist Mark Regnerus acknowledged that his study didn’t include children raised by same-sex couples in a stable relationship.
The study was financed by the New Jersey-based Witherspoon Institute, which says its mission is to help the public understand the ‘‘moral foundations’’ of democratic societies.
The American Psychological Association has said there’s no scientific basis for believing that gays and lesbians are unfit parents based on sexual orientation. But Regnerus believes it’s too early for sweeping statements.
‘‘We aren’t anywhere near saying there’s conclusive evidence’’ that children with same-sex parents grow up with no differences when compared to children with heterosexual parents, he said.
‘‘Until we get more evidence, we should be skeptical. . . . It’s prudent for the state to retain its definition of marriage to one man, one woman,’’ said Regnerus, who believes that’s the best scenario for children.
Regnerus will be cross-examined Tuesday.
The judge must determine whether there’s a rational public interest in restricting marriage to a man and a woman in Michigan. Experts testifying last week for nurses Jayne Rowse and April DeBoer said children simply need good parents, no matter their gender or sexual orientation.
Rowse and DeBoer of Hazel Park together are raising three adopted children with special needs. But they can’t marry in Michigan and, as a result, can’t jointly adopt each other’s children.
Earlier Monday, the judge barred an Ivy League law student from testifying at the trial, saying he might become an expert witness someday but his opinions wouldn’t help sway this case.
It was a blow for the Michigan attorney general’s office, which had offered Sherif Girgis as its first witness in defense of the state’s ban.
Girgis has written and talked about a historical defense of marriage between a man and a woman going back to ancient philosophers such as Cicero and Plato. He is pursuing a law degree at Yale University and a doctorate in philosophy in Princeton University.
‘‘The fact is you’re still a student. Someone else is still grading your papers,’’ said attorney Ken Mogill, co-counsel for two Detroit-area nurses challenging the gay-marriage ban.
Friedman said Girgis is smart, articulate, and bound to become an expert in his field, ‘‘but not quite yet.’’