Dr Robert Spitzer’s survey, published in 2001, looked at "reparative therapy" for homosexuals and was championed by religious and social conservatives in America as proof that gay people could successfully become straight, if they were motivated enough to do so.
However, the now retired Dr Spitzer has apologised in the same academic journal which originally published his study, calling it "fatally flawed".
In an interview with the New York Times, Spitzer, who is 79 and suffers from Parkinson's disease, described how he had written his letter of apology in the middle of the night after a visit from gay magazine journalist, Gabriel Arana, who told Spitzer he had been psychologically damaged by reparative therapy, and left the retired pyschiatrist questioning the study's validity.
Spitzer's study looked at the experiences of 200 people undertaking the therapy, who were asked a set of questions and had their reponses to the therapy and their feelings and sexual urges afterwards analysed. He concluded that many of them claimed some degree of change in their sexual desires.
The work made international headlines, as Spitzer had played a leading role 30 years previously in removing homosexuality from the list of mental disorders in the association's diagnostic manual.
Spitzer now admits his reasoning was wrong, writing in his letter of apology: "I believe I owe the gay community an apology for my study making unproven claims of the efficacy of reparative therapy…
"I offered several (unconvincing) reasons why it was reasonable to assume that the subject's reports of change were credible and not self-deception or outright lying. But the simple fact is that there was no way to determine if the subject's accounts of change were valid.”