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.
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.
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 among couples is the frequency of children secretly conceived with a different partner, leading to "non-paternities".
When they are not met, research has found that psychological damage can occur, including feelings of rage and betrayal, lowering of sexual and personal confidence, and damage to self-image.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.