1) I can't help but wonder how many females we have on this message board.
2) I don't blame them, considering they'd then get an ear-full of self-righteous judgment from people like Jaaaman if they answered affirmative. If they had nothing to gain out of it, why should they tell somebody about their private sex lives when he's just going to condemn them?

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A more recent study conducted in 1990 at the Kinsey Institute found that 27% of male and 24% of female college students had anal sex at least once.

One researcher offers a good point of comparison, as he surveyed his group of patients in the 1970s, and then a different group of his patients in the late 1980s. In the first survey 25% of women had anal sex (and 8% reported engaging in it regularly), and in the second, 72% had anal sex, and 23% reported engaging in it regularly.

A 1991 survey of 3200 men (in a nationally representative sample) found overall 20% of men aged 20-39 had engaged in anal sex at least once. 50% of the men who had tried it, had only tried it once. Interestingly, in this more contemporary study, older men reported having had anal sex than younger men (27% of men 35-39 versus 13% of men 20-24 years old).

The most recent data from a national representative sample comes from the 2002 National Survey of Family Growth (NSFG), conducted with over 12,000 men and women aged 15-44. 34% of men and 30% of women reported engaging in anal sex at least once.
Anal Sex Statistics – Data on the Prevalence of Heterosexual Anal Sex