information:classification
Prevalence of sexual monogamy

The prevalence of sexual monogamy can be roughly estimated as the percentage of married people who do not engage in extramarital sex. The Standard Cross-Cultural Sample describes the amount of extramarital sex by men and women in over 50 pre-industrial cultures. The amount of extramarital sex by men is described as "universal" in 6 cultures, "moderate" in 29 cultures, "occasional" in 6 cultures, and "uncommon" in 10 cultures. The amount of extramarital sex by women is described as "universal" in 6 cultures, "moderate" in 23 cultures, "occasional" in 9 cultures, and "uncommon" in 15 cultures.

Surveys conducted in non-Western nations (2001) also found cultural and gender differences in extramarital sex. A study of sexual behavior in Thailand, Tanzania and Côte d'Ivoire suggests about 16–34% of men engage in extramarital sex while a much smaller (unreported) percentage of women engage in extramarital sex. Studies in Nigeria have found around 47–53% of men and to 18–36% of women engage in extramarital sex. A 1999 survey of married and cohabiting couples in Zimbabwe reports that 38% of men and 13% of women engaged in extra-couple sexual relationships within the last 12 months.

Many surveys asking about extramarital sex in the United States have relied on convenience samples: surveys given to whoever happens to be easily available (e.g., volunteer college students or volunteer magazine readers). Convenience samples may not accurately reflect the population of the United States as a whole, which can cause serious biases in survey results. Sampling bias may, therefore, be why early surveys of extramarital sex in the United States have produced widely differing results: such early studies using convenience samples (1974, 1983, 1993) reported the wide ranges of 12–26% of married women and 15–43% of married men engaged in extramarital sex. Three studies have used nationally representative samples. These studies in 1994 and 1997 found that about 10–15% of women and 20–25% of men engage in extramarital sex.

Research by Colleen Hoffon of 566 homosexual male couples from the San Francisco Bay Area (2010) found that 45% had monogamous relationships. However, the Human Rights Campaign has stated, based on a Rockway Institute report, that "LGBT" young people... want to spend their adult life in a long-term relationship raising children." Specifically, over 80% of the homosexuals surveyed expected to be in a monogamous relationship after age 30.