The researchers argue these results have potential policy implications. "They reinforce the importance of rape shield laws that make information about victims' sexual histories and past behaviors inadmissible in court cases," they write. Photo by Florian Seefried/Getty Images

Sexism comes in a variety of forms, both subtle and overt. New research reveals that one of its oldest incarnations retains its pernicious power.

In a large survey of young American adults, women were evaluated less favorably as their perceived number of sexual partners increased. Needless to say, men were not.

"This challenges the claim that the sexual double standard ... only emerges in certain contexts, or when moderated by certain individual differences," writes a research team led by psychologist Michael Marks of New Mexico State University.

Rather, the phenomenon appears to be pervasive, as participants judged both close female friends and mere acquaintances more harshly if they perceived them as promiscuous.

The research, published in the journal Social Psychology, was designed to reconcile sometimes-conflicting laboratory studies about attitudes toward female promiscuity. It did so by asking participants to assess not hypothetical figures introduced as part of an experiment, but rather people they actually know.

The researchers recruited 4,455 participants via Amazon's Mechanical Turk website who were told they would take part in a study into their "perceptions of others." The team restricted participation to people ages 18 to 35, reasoning that the sexual double standard—in which men are rewarded for sexual activity, while women are punished—would be particularly relevant for young adults.

Each participant was directed "to think about either one male or one female friend or acquaintance whom they (a.) knew in their real life, and (b.) had information about their sexual history." Subjects then responded to 20 statements about this person, which evaluated them in terms of their values, success, intelligence, and likability.

Finally, they described the nature of their relationship with the person they were evaluating, and noted "how many people they thought the target individual had engaged in sexual intercourse with."

The results showed a clear pattern. Women were "increasingly derogated as the number of sexual partners increased," but men were not. This pattern held whether the people doing the judging were male or female.

"The sexual double standard was more pronounced as participants' certainty about the target's number of sexual partners increased," the researchers report. Still, the impact of this confidence was very small, meaning that women were judged more harshly even if the participants were relying on rumors or speculation.

Marks and his colleagues emphasize that participants were judging people they knew, and in some cases knew well; they thus had many sources of information to draw upon in forming a judgment of the person in question. Even so, perceived promiscuity played a significant role as participants made their evaluations.

One possible reason, the researchers speculate, is that women who reveal their sexual history "may be perceived as violating social norms, which may lead to less favorable evaluations." It's also possible many people may hold in their minds an arbitrary number of acceptable sexual partners for women, and start to look askance at any woman who surpasses it.

The researchers argue these results have potential policy implications. "They reinforce the importance of rape shield laws that make information about victims' sexual histories and past behaviors inadmissible in court cases," they write. Testimony that a victim had multiple sexual partners in the past could lead to a biased verdict.

Of course, there are countless other implications, none of them fair to women. But the sexual double standard reflects deeply ingrained ideas and assumptions. Moving beyond it will require "loosening the hold of these norms and stereotypes," the researchers conclude, "which is something that will likely take generations."