Studies suggest around 30–40% of unmarried relationships and 18–20% of marriages see at least one incident of sexual infidelity.
Sex ratio theory is a theory that explains the relationship and sexual dynamics within different areas of the world based on the ratio of the number of marriage-aged men to marriage-aged women.
According to this theory, an area has a high sex ratio when there is a higher number of marriage-aged women to marriage-aged men and an area has a low sex ratio when there is more marriage-aged men to marriage-aged women.
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 father (or mother).
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.
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.
Article uses three different citation styles: inline footnotes, a "references section" and a "further reading" section. For example, the first citation, Leeker & Carlozzi, points to the further reading section. 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.
The second citation (Weeks) is both defined in text and pointed at using a footnote. 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.
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".
Those that posit a sex difference exists state that men are 60% more likely to be disturbed by an act of sexual infidelity (having one's partner engage in sexual relations with another), whereas women are 83% more likely to be disturbed by an act of emotional infidelity (having one's partner fall in love with another).
Strategic pluralism is a theory that focuses on how environmental factors influence mating strategies.