MONDAY, Aug. 16 (HealthDay News) -- A new study finds that men are more likely to cheat if their income is much lower than what their wife or female partner makes, while women are more likely to fool around if they make more than their husband or male partner.

The findings suggest that disparities in moneymaking play a significant role in infidelity, at least among the young couples they studied.

"With women, they were less likely to engage in infidelity the less money they make relative to their husband," said study author Christin Munsch. "But for men, the less money you make relative to your spouse, the more likely you are to engage in infidelity."

Munsch, a graduate student at Cornell University, said she came up with the idea of studying the effects of income on infidelity after hearing from a friend who has cheated on his partner. He told Munsch that "she made all the money, she had all the friends, and he'd moved up there to be with her. He felt completely powerless."

While there's been previous research into infidelity, it didn't look into differences in income among couples, Munsch said.

So she examined the results of a national survey that tracked 9,000 people beginning in 1997 when they were children. She focused on the results of the survey from 2001-2007, when the participants were between 17 and 27 years old.

The findings are scheduled to be released Monday at the American Sociological Association annual meeting in Atlanta.

Munsch found that almost 7 percent of the men reported having sex outside their relationships between 2002 and 2007, while about 3 percent of women did. Black and Hispanic men were more likely than white men to have fooled around.

Two lifestyle factors, higher education and regular religious observance, seem to help keep infidelity at bay for both men and women, the study found.

But factors having to do with money -- such as the man making more or less than his wife or female partner -- did increase the risk of infidelity, Munsch said. But she cautioned that "we're talking about very small numbers."

If you're a woman and "you make more money than your partner, your partner isn't 100 percent likely to cheat," she stressed.

Still, money appeared to be a significant factor.

Men who make less than their wives may lean toward infidelity because they feel a "gender identity threat," Munsch speculated.

"The range of acceptable behaviors for men is a lot narrower" when it comes to dynamics in a relationship, such as those involving finances, she said. "It's harder to hit that mark because it's a smaller mark. If you're not hitting the mark, you might feel threatened."

On the other end of the spectrum, infidelity seemed to rise when one partner made a lot more money than the other. And that held true whether the man or the woman was the big wage earner.

"If you work long hours and have more disposable income, it's easier to hide infidelity," Munsch reasoned. For example, unusual expenses charged to credit cards might go unnoticed. Also, she said, people who make more money may also travel frequently and meet lots of people of the opposite sex.

Helen Fisher, an anthropologist and research professor at Rutgers University, said it makes sense that men with more money would be more likely to fool around.

"He probably travels a lot and drives nicer cars, and he's probably in finer restaurants. He's advertising the kind of resources that women are looking for from an evolutionary perspective," she said. "Around the world, women go for men who are on the top of the pile."

But there's less reason, from an evolutionary perspective, for a man to stray if he makes less money than his female partner, she said. "You'd think a man would want to stick around those resources himself. That may have more of a purely psychological explanation."

As for women, she said, wealth brings them a greater power to do what they want, whether it's leave a bad relationship or have an affair.

More information

The U.S. National Library of Medicine has details on divorce, the end product of some infidelity.