I read the article on the train, so I don’t remember all the details (though I think it was 4 or 5 sex partners for women and some 3 or 4 more for men, which makes the 75 percent difference seem greater than it is). Two additional hypotheses to the ones already brought forth: 1. A statistically, if not numerically, significant number of the male respondents have bonked a large number of prostitutes. My impression (from their writing) is that they typically cover at least 5 women over a weekender in Prague or wherever; I read somewhere that about 1 million German men pay visit to a cathouse at least once a week — prostitution is legal in Germany — you do the maths; 2. The hunch amongst my friends and I is that women, on average, have had fewer sex partners than men, but that there is a greater discrepancy on the male side (i.e. a great number of men have had very few sexual encounters and a small number of men have had a great many). I could imagine that the kind of men who would lower the mean value in these kinds of surveys are the exact ones that would hesitate to participate, for any number of reasons.