8 months, while the average duration of the second was 29.6 months. Thus, the relationships studied were mostly serious and of substantial duration. No one was married at the start of the project, but some would have married that first partner or the second during the time frame of the study. For the most part, however, it is best to think about these findings in the context of the stage of life in which people are often seriously involved, but not yet married-a stage of life that has grown substantially in the past few decades.

At each time point (which tended to be every four-to-six months), participants were asked, “Have you had sexual relations with someone other than your partner since you began seriously dating?” Participants were also asked if they had either known or suspected their present partner of having sex with someone else. Obviously, there are biases when people self-report such behavior, but that’s a problem for the entire literature. Further, the specific questions used in this study may exclude emotional affairs, as well as some online affairs in which there is some sexual aspect, but the respondents tell themselves they are not actually having sex. (Also, in such a sample there would be some small percentage of people who would have been in some sort of consensual non-monogamous arrangement, in which having sex with someone outside the relationship would not be the same as cheating, because there was some agreement about this. )

Forty-four percent of this sample reported having had sex with someone other than their present partner in one or both of the relationships studied

Knopp and colleagues controlled for some of the variables known to be associated with a greater and lower risk of being unfaithful, net of other factors like relationship quality and commitment to one’s partner. Read More >