Men in China have elevated odds of having had nontransactional premarital sex and of testing positive for an STI if age-matched women are relatively abundant in their communities, according to a national study on the relationship between sex ratios and men's sexual risk behaviors.1 Moreover, men who live in communities with higher ratios of females to males have decreased odds of having engaged in transactional sex. Extrapolating from these findings, the researchers suggest that the continuing masculinization of China's sex ratio may reduce men's risk of engaging in nontransactional premarital sex and of contracting an STI, while increasing the likelihood of their having intercourse with a sex worker.

China has had an unequal sex ratio at birth for decades, and this imbalance grew substantially between 1982 and 2001, from 93 to 85 girls per 100 boys. Few studies have examined how a deficit of women influences men's sexual risk behaviors and STI risk. This study used individual-level data from the 1999–2000 Chinese Health and Family Life Survey (CHFLS) and sex ratio measures from national censuses conducted in 1982, 1990 and 2000. The analytic sample consisted of 1,023 nonmigrant male CHFLS respondents aged 20–44, most of whom provided a urine sample for STI testing. To standardize the data for men born in different decades, and to restrict the sex ratio calculations to individuals of similar age, the researchers calculated the community-level sex ratio as the ratio of women aged 15–21 to men aged 17–23 in each respondent's community when he was 20 years old. Separate logistic regression models were used to identify associations between the sex ratio and three sexual risk outcomes: having ever had nontransactional premarital sex, having ever had transactional sex (regardless of marital status) and testing positive for an STI (gonorrhea, chlamydia or trichomoniasis).

Forty-eight percent of respondents were born in the 1970s, while 38% were born in the 1960s and 14% in the 1950s. On average, 49% of the population in men's communities resided in urban areas, and the mean sex ratio was 90 females per 100 males. One-fourth of respondents had had nontransactional premarital sexual intercourse, 9% had engaged in transactional sex and 4% tested positive for gonorrhea, chlamydia or trichomoniasis.

Regression analysis revealed that an increase in the sex ratio of one woman per 100 men was associated with a 1.5% increase in the odds that a man had engaged in nontransactional premarital intercourse. At this rate of change, a reduction in the sex ratio of eight women per 100 men—roughly the change in China's sex ratio at birth from 1982 to 2001—would result in an 11% decline in the odds that a man had had nontransactional premarital intercourse. Compared with men born in the 1950s, those born in the subsequent two decades were more than twice as likely to have had such sex (odds ratios, 2.5 and 2.8, respectively).

By contrast, the odds that a man had engaged in transactional sex declined by 2% for every additional woman per 100 men, though this association just missed statistical significance (p=.053). At this rate, a reduction in the female-to-male sex ratio of eight women per 100 men would increase the odds that a man had had transactional sex by 17%. Men born in the 1970s were more likely than those born in the 1950s to have had transactional sex (odds ratio, 2.2). In the final regression analysis, an increase in the sex ratio of one woman per 100 men was associated with a 3% increase in the likelihood that a man would test positive for an STI; a decrease of eight women per 100 men would reduce the odds of a positive test by 22%.

Together, these findings suggest that the shortage of women in China increases the likelihood that men will engage in transactional sex, but decreases their odds of contracting an STI. Further analysis found that men who had had transactional sex were, in fact, more likely than others to test positive for an STI (odds ratio, 3.3), but that the increase in STI risk resulting from transactional sex was outweighed by a reduction in STI risk resulting from the decline in nontransactional premarital sex. Additional analyses revealed no evidence of confounding cohort or community effects on the sexual risk outcomes.

The researchers note that, in contrast to speculations that China's declining female-to-male sex ratio will lead to increased prevalence of HIV and other STIs, their study found that men were less likely to test positive for STIs when relatively fewer women were available for sexual relationships or marriage. However, they identified several limitations of the study: the inability to date the timing of respondents' sexual behaviors, the lack of complete residential histories and the unknown influence of sex ratio on frequency of intercourse and prevalence of extramarital sex or multiple partnerships. The authors recommend that future research examine women's sexual behavior—which may counterbalance men's behavior—and explore "the consequences of imbalanced sex ratios for men's and women's sexual health behavior in … other countries [such as India] that are experiencing a numerical deficit of women."

—J. Thomas



1. South SJ and Trent K, Imbalanced sex ratios, men's sexual behavior, and risk of sexually transmitted infection in China, Journal of Health and Social Behavior, 2010, 51(4):376–390.