"We think everybody is out there doing it," says Janet Lever, a sociologist at California State University, Los Angeles, and the study's lead researcher. "Well, they're not."
In fact, the rate of cheating has stayed pretty consistent, according to research expert Tom W. Smith, director of the General Social Survey for the National Opinion Research Center at the University of Chicago.
Smith conducted the highly respected study "American Sexual Behavior," a poll of 10,000 people over two decades. The study found that 22 percent of married men and 15 percent of married women have cheated at least once similar to the results from the MSNBC.com/iVillage survey.
Still, much of this depends on your definition of cheating.
Nearly everybody considers sexual intercourse or oral sex to be cheating, but there are some other behaviors that fall into grayer areas.
Nearly 20 percent of survey takers in committed relationships have romantically kissed someone else, a breach that 83 percent of people consider to be cheating.
And 15 percent of men (though only 7 percent of women) have engaged in online sex or sexual Webcamming, which 66 percent of people consider to be cheating.
Blind to the affair
Ironically, while we tend to overestimate cheating in society, we are often blind to it in our own lives. If your partner is cheating, chances are, you have no idea.
Six in 10 cheaters believe they totally got away with their affair and another one in 10 felt their partner was suspicious, but never found out for sure. Few cheaters were busted in the act. And even when confronted with a partner's suspicions, only 6 percent of both men and women confessed to having an affair.