Large-scale observations of human sexuality were started by Alfred Kinsey and co-workers in the United States in 1941. Their work was expanded in 1947 with the founding of the Kinsey Institute. Kinsey was professor of zoology at Indiana University, when, in 1938, he was asked to teach marriage preparation classes. It was then that he realized how little truly scientific data existed on human sexual behavior. More than 18 000 interviews were conducted and a tremendous amount of data collected. Many original observations and publications on human sexual response, function and dysfunction as well as sexual behavior were based on these data. Many of these observations are still true today, but some are not because (1) the methodology used was not appropriate; (2) sexual behavior is a biological, psychologic and social phenomenon — as the society changes so do some aspects of sexuality.

Kinsey noted that in men social class is an important determinant of sexual behavior. Working-class men would experience sexual intercourse at an early age and engage much less in petting and oral sex. Once married, they would become involved in extramarital affairs early on in the marriage, but less so when getting older. Upper-class men would be more likely to engage in petting and oral sex. They tended to be faithful until middle age, when they might seek extramarital opportunities.

For women, social class was found to have a smaller impact on sexual behavior. Kinsey noted that some women could go through long periods of sexual inactivity. He concluded that men are more responsive to psychologic stimuli (fantasies and visual cues), while women require more tactile stimulation, though they also respond to visual, sexually explicit material. Kinsey reported that almost all men and 75% of women had masturbated at some stage in their lives.

Research into the epidemiology of sexual function continues, and the results of two cross-sectional studies of women in the UK and the United States are presented in Table Results of two cross-sectional studies investigating sexual disorders in women in the UK and the United States. The UK study found that sexual interest in women varies across social classes. Impaired sexual interest was reported by 12% of classes I-II; 18% in class III; and 15% in classes IV-V. There was no correlation of sexual dysfunction to menopausal symptoms. A history of psychiatric problems was reported by 10% of those reporting sexual dysfunction. Age, marital problems and neurotic predisposition were identified in 72% of cases. Interestingly, even though 33% of participants were found to have some form of sexual dysfunction, only 10% identified themselves as having sexual problems, and this was not related to age. Even more remarkable, only 4% said that they would commence treatment if available. The American study found that single people were more likely to have an orgasmic disorder than married ones. High educational attainment was found to be associated with fewer sexual problems in both sexes. Risk factors for sexual problems were stress and a deteriorating economic position (expressed as a decline in household income). Arousal disorders were frequently found in women with adult-child sexual contact or forced sexual contact. Sexual problems were more prevalent in younger women and older men.

Table Results of two cross-sectional studies investigating sexual disorders in women in the UK and the United States

Problem Study 1 (%)* Study2(%)**
Impaired sexual interest 17 30
Impaired arousal 17 21
Impaired orgasm 16 25
Dyspareunia 8 16
Any sexual dysfunction 33 43
Sex not pleasurable 19
Anxiety about performance 11
Help seeking 4 20

* Comprising 436 sexually active women aged between 35 and 59 years; ** comprising 1749 sexually active women aged between 18 and 59 years

One American cross-sectional study of adults aged 60-85 years found that 69% of men and 30% of women were sexually active, married ones more so than unmarried ones. Among married couples 74% of men and 56% of women were sexually active. The corresponding figure for single individuals was 31% for men and 5% for women. Sexual activity correlated with incontinence, poor mobility, heart problems and sedatives. Among married men, 30-65% were impotent, depending on age.

It is evident from many studies that the main sexual problem in women is lack of desire, while in men it is erectile dysfunction.

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