Why do men cheat? And for that matter, why do women?

Robin Milhausen, a sex researcher at the University of Guelph in Ontario, doesn't claim to have all the answers, but she joined forces with two other professors to shed a little light on the subject.

Their study, based on surveys of 918 heterosexual men and women in monogamous relationships, found that 23 percent of male respondents and 19 percent of female respondents reported having cheated on their current partner. The researchers defined infidelity as a sexual interaction "with someone other than your primary partner that could jeopardize, or hurt, your relationship."

Milhausen and her colleagues, whose findings were recently published in the Archives of Sexual Behavior, were interested in personality and relationship factors associated with cheating.

For women, they found low relationship satisfaction often was tied to infidelity. Women who were unhappy in their relationships were 2.6 times more likely to cheat than women who were satisfied. Women who reported being incompatible with their partner in terms of sexual values and attitudes were 2.9 times more likely to have an affair.

One of the findings that surprised Milhausen most was that men who reported higher rates of sexual inhibition because of performance anxiety were more likely to cheat. "If you have sex with someone outside of your relationship, you'll never have to see them again," she says. "You won't have those problems with wounded pride or ego."

Men and women who were less concerned about the consequences of their sexual behavior were more likely to cheat. Still, Milhausen cautions, none of these factors is a guaranteed predictor of infidelity or faithfulness.

Her take-away from the report is that people who want to avoid affairs should be as honest as possible about their needs. "What do you need to be satisfied in this relationship for the next 50 years?" she asks. "Way more couples need to have those discussions."