The book Sperm Wars raported about interesting research about number of sex partners. Is is well-known that men raport double the amount of sex partners than women. People typically think men exaggerate the numbers. Researchers hooked men and women to lie detectors, and while number of sex partners reported by men dropped a little, the number of sex partners reported by women raised a lot, and they were practically equal. I think the social stigma for women is higher for number of partners, and that explains the tendency to downplay them somewhat.