Orgasm is the climax of sexual arousal, during which both sexes experience contraction of muscles and blood vessels in the pelvic area. While male orgasm is medically and physiologically well understood, female orgasm has remained problematic. Freudian and other theories about female sexuality have historically valorized female orgasm in coitus over climax achieved by stimulation of the clitoris. Orgasm, particularly in women, is difficult to study by the survey method because of biases introduced by self-selection, self-reporting, and, not infrequently, those imposed by subject selection and research design.