From The New York Times:
If you cheated on your spouse, would you admit it to a researcher?
That question is one of the biggest challenges in the scientific study of marriage, and it helps explain why different studies produce different estimates of infidelity rates in the United States. Surveys conducted in person are likely to underestimate the real rate of adultery, because people are reluctant to admit such behavior not just to their spouses but to anyone. In a study published last summer in The Journal of Family Psychology, for example, researchers from the University of Colorado and Texas A&M surveyed 4,884 married women, using face-to-face interviews and anonymous computer questionnaires. In the interviews, only 1 percent of women said they had been unfaithful to their husbands in the past year; on the computer questionnaire, more than 6 percent did.
At the same time, experts say that surveys appearing in sources like women’s magazines may overstate the adultery rate, because they suffer from what pollsters call selection bias: the respondents select themselves and may be more likely to report infidelity. But a handful of new studies suggest surprising changes in the marital landscape. Infidelity appears to be on the rise, particularly among older men and young couples. Notably, women appear to be closing the adultery gap: younger women appear to be cheating on their spouses nearly as often as men.
More here.