Men generally report more opposite-sex partners than women, sometimes even twice as much. But a new study suggested social expectations and a tendency to "estimate," rather than "count," may be causing men to exaggerate.

The findings of the study were published in the Journal of Sex Research on July 25.

"Scientists researching sexual behavior generally have to rely on what people tell them," said co-author Dr. Kirstin Mitchell, a research fellow at the University of Glasgow, Scotland. "Accurate reporting of sexual partners is crucial for many reasons, including assessing individual risk of sexually transmitted infections (STIs) and estimating the rate of STI/HIV transmission."

As part of a survey interviewing people in the 16-74 age range, 6,023 men and 7,170 women from Britain were asked  how many sexual partners they’ve had, how they arrived at the number, and their attitudes about sex.

Looking at the number of partners, the team found men reported a mean of 14.4-lifetime partners while women reported 7.12. Research over the years has found men, on average, report nearly twice as many sexual partners as women.

"The interesting thing about opposite-sex lifetime partners is that statistically, the average number reported by men and women should be the same," Dr. Mitchell said.

The reason for the gender gap, she suspected, may have had to do with the "accounting strategy" or the way the numbers were determined. Men were more likely to use a rough estimate of how many partners they have had. On the other hand, women were inclined to count each partner as they are "more likely to keep an ongoing tally in their head," she said.

When looking at the respondents who reported having five to nine partners, it was found 24 percent of men estimated their number of partners compared to 15 percent of women. Whether a person is more likely to exaggerate or understate their number may be influenced by their attitudes about sex.

In general, women had more conservative attitudes about sex than men. About 18 percent of the male respondents viewed one-night stands as "not wrong at all" compared to 9 percent of female respondents, and 65 percent of women thought it was "always wrong" when a married person had sexual relations with someone other than their partner, while the figure was 57 percent among men.

"[Social expectations for] men to be sexually active and women to be sexually chaste still has an influence," Dr. Mitchell said.

The pressure to conform to these expectations are a major factor in misreported data.

But she noted the good news, highlighting how trends have shown this gender gap to narrow over time, suggesting these norms are slowly falling out of favor.