Study sheds new light on sex survey 'imbalance'

Scientists believe they have discovered why sex surveys repeatedly find that men claim to sleep with more women than is mathematically possible.

Scientists believe they have discovered why sex surveys repeatedly find that men claim to sleep with more women than is mathematically possible.

Sex surveys worldwide show an apparent imbalance between the number of sexual partners claimed by heterosexual men and those claimed by heterosexual women.

Mathematically the two should balance out, with the same average number for men as for women, but for some reason men always seem to have had more sexual contacts than women.

In the past, this has been put down to male boastfulness - men over-reporting the number of girlfriends they have had - and female coyness - under-reporting their change of boyfriend.

But Devon Brewer, a researcher at the University of Washington's alcohol and drug abuse institute has found evidence of a "third way" of explaining the discrepancy.

In a study published in the Proceedings of the National Academy of Sciences, he found that prostitutes have been under-represented in many of the sex surveys in the world, included those in Britain.

Men paying for sex with professional women who have a disproportionately high number of sexual partners could easily account for the imbalance between typical heterosexual males and females, Dr Brewer said.

"Generally speaking, sampling procedures used in these surveys exclude the lodgings where women working as prostitutes tend to live, like motels, rooming houses and homeless shelters. Once the prostitutes' high number of sexual partners was factored in, the discrepancy disappeared," Dr Brewer said.

The explanation has been disguised because although men appear to be happy to add prostitutes to their total number of sexual conquests, they are unlikely to admit that they paid for sex.