As a result of this scientific research, the American Psychiatric Association declassified homosexuality as a mental disorder in 1973. That research and subsequent studies consistently failed to produce any empirical or scientific basis for regarding homosexuality as anything other than a natural and normal sexual orientation that is a healthy and positive expression of human sexuality. The American Psychiatric Association listed homosexuality in the Diagnostic and Statistical Manual of Mental Disorders (DSM) in 1952, but that classification came under scrutiny in research funded by the National Institute of Mental Health. The field of psychology has extensively studied homosexuality as a human sexual orientation.
