For example, one study found that some women in more financially independent and higher positions of power, were also more likely to be more unfaithful to their partners.These findings suggest there may be various factors that might influence the likelihood of some individuals to engage in extradyadic relationships, and that such factors may account for observed gender differences beyond actual gender and evolutionary pressures associated with each.Studies suggest around 30–40% of unmarried relationships and 18–20% of marriages see at least one incident of sexual infidelity.
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.
According to The New York Times, the most consistent data on infidelity comes from the University of Chicago's General Social Survey (GSS).
Interviews with people in non-monogamous relationships since 1972 by the GSS have shown that approximately 12% of men and 7% of women admit to having had an extramarital relationship.
In terms of infidelity, the theory states that when sex-ratios are high, men are more likely to be promiscuous and engage in sex outside of a committed relationship because the demand for men is higher and so this type of behaviour, which is desired by men, is more accepted.
On the other hand, when sex ratios are low, promiscuity is less common because women are in demand and since they desire monogamy and commitment, in order for men to remain competitive in the pool of mates, they must respond to these desires.
Results, however, vary year by year, and also by age-group surveyed.
For example, one study conducted by the University of Washington, Seattle found slightly, or significantly higher rates of infidelity for populations under 35, or older than 60.
One measure of infidelity among couples is the frequency of children secretly conceived with a different partner, leading to "non-paternities".
Such covertly illegitimate children amount to about 1–2% of newborns in European 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 father (or mother).