In general, national surveys conducted in the early 1990s reported that between 15–25% of married Americans reported having extramarital affairs.
People who had stronger sexual interests, more permissive sexual values, lower subjective satisfaction with their partner, weaker network ties to their partner, and greater sexual opportunities were more likely to be unfaithful.
It is more common for men compared to women to engage in extradyadic relationships.
The National Health and Social Life Survey found that 4% of married men, 16% of cohabiting men, and 37% of dating men engaged in acts of sexual infidelity compared to 1% of married women, 8% of cohabiting women, and 17% of women in dating relationships.
In one study, rates were higher in more recent marriages, compared with previous generations; men were found to be only "somewhat" more likely than women to engage in infidelity, with rates for both sexes becoming increasingly similar.
Another study found that the likelihood for women to be involved in infidelity reached a peak in the seventh year of their marriage and then declined afterwards; whereas for married men, the longer they were in relationships, the less likely they were to engage in infidelity, except for the eighteenth year of marriage, at which point the chance that men will engage in infidelity increases.
Such covertly illegitimate children amount to about 1–2% of newborns in studied populations.One measure of infidelity is covert illegitimacy, a situation which arises when someone who is presumed to be a child's father (or mother) is in fact not the biological parent.Frequencies as high as 30% are sometimes assumed in the media, but research Such studies show that covert illegitimacy is in fact less than 10% among the sampled African populations, less than 5% among the sampled Native American and Polynesian populations, less than 2% of the sampled Middle Eastern population, and generally 1–2% among European samples.There is currently debate in the field of evolutionary psychology whether an innate, evolved sex difference exists between men and women in response to an act of infidelity; this is often called a "sex difference".Studies show that 90% of cheaters are men, with the remaining 10% women.Infidelity (synonyms include: cheating, adultery (when married), netorare (NTR), being unfaithful, or having an affair) is a violation of a couple's assumed or stated contract regarding emotional and/or sexual exclusivity.Other scholars define infidelity as a violation according to the subjective feeling that one's partner has violated a set of rules or relationship norms; this violation results in feelings of sexual jealousy and rivalry.In that study which involved 19,065 people during a 15-year period, rates of infidelity among men were found to have risen from 20 to 28%, and rates for women, 5% to 15%.A survey conducted in 1990 found 2.2% of married participants reported having more than one partner during the past year.Studies suggest around 30–40% of unmarried relationships and 18–20% of marriages see at least one incident of sexual infidelity.Rates of infidelity among women are thought to increase with age.