From Feministe, among others, comes this story of a study testing for a correlation between a "dark triad" of negative personality traits (narcissism, impulsiveness and deceitfulness).
The sample was entirely college students. College students, while they're easy to get as samples (just make the study mandatory for an intro psych class), are not representative, because:
- They skew young - teens and early 20s. Younger people are more likely to be susceptible to both manipulation and to societal messages about these traits. (Similar to how there's a difference between a Nice Guy(TM) and a good man, there's a difference between a Bad Boy(TM) and an asshole.)
- They skew privileged - healthy, wealthy and (primarily) white.
- They may skew with respect to personality. If being narcissistic, impulsive or exploitative makes it tougher to get into college, then the ones who do may be more likely to have some compensating characteristic.
- They're asking about total number of partners, not partners over a given time period. Especially when you're talking about college students, total number of partners is heavily dependent on age of first sexual activity.
- The number is self-reported - it's not inconceivable that the "dark triad" personalities are more likely to lie about the number.
- The write-up conflates number of partners and desirability, which assumes that all these encounters were of the "enthusiastic consent" sort. (Especially since this correlation seems to be especially true of men.)
- It's also quite possible that those "dark triad" personalities are the sort that buy in to the "number of partners is your score," and so make more of an effort to increase the number for its own sake.
- The write-up also conflates number of partners and frequency of sex, which may not be - lots of people are in monogamous sexual relationships, which get counted as "one," just the same as a one-night stand, even though the amount of sex is very, very different.