In 1952, the American Psychiatric Association listed homosexuality in the "Diagnostic and Statistical Manual" ("DSM") as a mental disorder. A large-scale study of homosexuality in 1962 was used to justify inclusion of the disorder as a supposed pathological hidden fear of the opposite sex caused by traumatic parent–child relationships. This view was widely influential in the medical profession. In 1956, however, the psychologist Evelyn Hooker performed a study that compared the happiness and well-adjusted nature of self-identified homosexual men with heterosexual men and found no difference. Her study stunned the medical community and made her a hero to many gay men and lesbians, but homosexuality remained in the "DSM" until 1974.