This was an interesting statistic, from the Institute of Family Studies:
Basically, at least according to the results of this survey (including how many lies I don’t know), there are a lot fewer ho-hos than we usually think. Even in the decadent 1970s, 21% of all women were virgins at marriage, and 43% had only one previous partner — in many cases, probably the man she married. Only 2% (supposedly) had 10+ partners. It’s too bad we don’t have numbers for the 1960s and 1950s.
Today, of course, the numbers are pretty badly skewed toward the 10+ range. The 18% number is in line with anecdotal evidence that about 20% of women today (or, maybe 15 years ago) were sluts. However, the good girls are gone quickly. They form lasting relationships at a young age, and get married. If you look among the single women remaining after age 26, there are a lot of sluts, hoes, and single moms. If 18% of women have 10+ partners at marriage, but none of these girls (typical) begin a relationship leading to marriage before Age 26, then 36% of the leftovers are Sluts and Hoes. Plus, the Single Moms and Fuglies — a category that grows over time, as there are many women who look good at 19 but not so much at 28.
In practice, the Slut cutoff is around 15-20 partners, I think. This is about the point at which women become incapable of forming a lasting monogamous relationship. So, it is not arbitrary, but reflects some kind of brain chemical change in women.