Her work argued that a false correlation between homosexuality and mental illness had formed the basis of classifying homosexuality as a mental disorder by studying only a sample group that contained homosexual men with a history of treatment for mental illness. This is of critical importance in refuting cultural heterosexism because it argues that homosexuality is not developmentally inferior to heterosexuality. Her demonstration that it is not an illness led the way to the eventual removal of homosexuality from the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders.