?Believe it or not, despite what you may think, good sex typically lasts 13 minutes or less, not counting foreplay.

Penn State Erie researchers Eric Corty and Jenay Guardiani surveyed members of the Society for Sex Therapy and Research, which includes psychologists, physicians, social workers, marriage/family therapists and nurses who have collectively treated thousands of patients over several decades.

"A man's or woman's interpretation of his or her sexual functioning as well as the partner's relies on personal beliefs developed in part from society's messages, formal and informal," the researchers said. "Unfortunately, today's popular culture has reinforced stereotypes about sexual activity. Many men and women seem to believe the fantasy model of large penises, rock-hard erections and all-night-long intercourse."

A total of 34 experts responded to the survey and were asked what they thought was the optimal time for intercourse, from penetration to ejaculation.

On average, the respondents in this relatively small survey ranked a duration of 3 to 7 minutes as adequate and 7 to 13 minutes as desirable. Anything less was considered, on average, to be too short and anything more, too long.

Past research has found that a large percentage of men and women say they want sex to last 30 minutes or longer, the researchers say.

"This seems a situation ripe for disappointment and dissatisfaction," said lead author Eric Corty, associate professor of psychology. "With this survey, we hope to dispel such fantasies and encourage men and women with realistic data about acceptable sexual intercourse, thus preventing sexual disappointments and dysfunctions."

(Agencies via Xinhua April 2, 2008)