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In 1953 Dr. Evelyn Hooker investigated the commonly held belief that homosexuals were mentally ill. This podcast interview with Hooker provides a first hand account and focuses on her ground-breaking study and the origin of the research concept, including NIMH approval and other hurdles. Here's an APA overview of Hooker's study, which was published in 1958.
The Diagnostic and Statistical Manual of Mental Disorders was initially published in 1952 as a 132 page resource for use by U.S. healthcare professionals. Expanded and revised with each subsequent edition, the DSM (as it is informally known) handbook incorporates the efforts of hundreds of international experts and is influential globally as the authoritative guide to the diagnosis of mental disorders. The DSM defines and classifies mental disorders and provides descriptions, symptoms, and other criteria to better improve diagnosis, treatment, and future research. A close study of successive editions of the DSM reveals changing understanding of gender in psychology and psychiatry. One example of the significance, though Hooker's research was published in 1958, it was another 17 years before the APA altered the DSM to reflect the research findings.