All the surveys on sexual behaviour to date conclude that men have up to four times as many female partners as can be accounted for when women are interviewed on the same subject, said Professor Martina Morris, a sociologist at Columbia University in New York.
Most people are honest for most of the time when answering questions about their sexual history, she said. The overstatements almost entirely emanate from a small minority of men who claim to have had unusually high numbers of partners.
The discrepancy between what men and women say about their numbers of partners has called into question the validity of sexual behaviour surveys, which are used to predict the spread of diseases such as Aids, Professor Morris said.
Because surveys indicated that men have nearly four times as many female partners as women seem to admit to, sexologists were forced to conclude either that 60 per cent of the men's contacts were 'missing', or that every man interviewed had exaggerated his sexual history.
One suggestion was that 'men like to brag, and women like to hide' their sexual histories, Professor Morris said. But when she analysed the most active people in sex surveys, she found that they accounted for nearly all of the discrepancy, indicating the rest were largely honest.
Men with many sex contacts tend to 'round up' their estimates of how many women they have had, primarily because they could not remember, but also because they liked to boast. Equally, the most active females tend to round down their estimates. This introduces a 'reporting bias', Professor Morris said.