(AP) -- A prominent retired psychiatrist is apologizing to the gay community for a decade-old study that concluded some gay people can go straight through what's called reparative therapy.

Dr. Robert L. Spitzer, formerly of Columbia University, now says he no longer believes his work showed that.

For the study, Spitzer had interviewed 200 people who'd claimed some degree of change. The "fatal flaw" is that there is no way to judge the credibility of their accounts, Spitzer says in a letter he submitted last month to a journal that published his work in 2003.

The work made headlines when he presented it at a 2001 meeting of the American Psychiatric Association. One reason for the attention was that Spitzer had played a leading role 30 years before in removing homosexuality from the list of mental disorders in the association's diagnostic manual.

Spitzer's study was attacked by critics who questioned the reliability of the accounts from the people he interviewed. At the time, Spitzer acknowledged that he had no proof their stories were accurate, but said several aspects of their accounts suggested their statements could not be dismissed out of hand.

Now he says his reasoning was wrong, and that "there was no way to determine if the subject's accounts of change were valid," he wrote in a letter to the editor of the Archives of Sexual Behavior. Spitzer, who lives in Princeton, N.J., sent a copy to The Associated Press after a reporter interviewed him about his change of heart.

"I believe I owe the gay community an apology for my study making unproven claims of the efficacy of reparative therapy," Spitzer wrote. "I also apologize to any gay person who wasted time and energy undergoing some form of reparative therapy because they believed that I had proven that reparative therapy works with some `highly motivated' individuals."

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