A study of young married Americans finds people who are economically dependent on their spouse are more likely to have an affair.

You’ve heard of the seven-year itch. But when it comes to infidelity, a more important factor is probably the 70 percent ratio.

That’s one finding of a new study that looks at patterns of infidelity among young married Americans. It finds husbands who contribute 70 percent of the household income are the least likely to cheat on their wives.

Above that figure, the chances of him being unfaithful go up a little. But the further a man falls below that threshold—which is to say, the more economically dependent he becomes on his wife—the odds of him having an affair increase significantly.

That’s one conclusion of University of Connecticut sociologist Christin Munsch, who analyzed data on 2,757 married Americans between the ages of 18 and 32. Writing in the American Sociological Review, she finds a strong relationship between spouses’ relative incomes and their chances of cheating.

"Infidelity may allow economically dependent men to engage in compensatory behavior while simultaneously distancing themselves from breadwinning spouses."

“For both (young) men and women, economic dependency is associated with a higher likelihood of engaging in infidelity,” she writes, adding that this dynamic is far stronger among males.

“For men, dependence may be particularly threatening,” she notes. “Infidelity may allow economically dependent men to engage in compensatory behavior while simultaneously distancing themselves from breadwinning spouses.”

Munsch used data from the National Longitudinal Survey of Youth, a nationally representative sample of approximately 9,000 Americans who were 12 to 16 years old as of December 31, 1996. She specifically looked at responses of married participants collected between 2001 and 2011.

While the survey did not specifically ask participants if they had cheated on their spouse (presumably because many would not answer honestly), Munsch identified infidelity by looking at answers to related questions such as “How many partners have you had intercourse with since the last interview?” and “Since the last interview, have you had sex with someone who was a stranger?”

Munsch measured each couple’s relative income by subtracting the partner’s income from the respondent’s income, and dividing that number by the pooled marital income. She also factored in several variables that could contribute to marital instability, including the number of children in the household, and the average number of hours participants worked per week.

One of her more interesting findings: Women who were the primary breadwinners of a household were less likely to cheat than women who were dependent on their husband’s income. This proved true in spite of the fact that their income-producing status can cause their husband to feel threatened, and increase the odds he will have an affair.

Munsch argues this reflects an attempt to “keep potentially strained relationships intact” by “neutralizing their gender deviance.” In other words, they’re aware that their stereotype-defying position threatens their marriage, and they don’t want to do anything to increase the odds of a break-up.

The results suggest outmoded gender norms continue to drive our expectations, sometimes in relationship-threatening ways. But Munsch believes this is likely a temporary situation.

“This does not necessarily mean that as women’s wages and relative earnings rise, marriages will become less stable,” she writes. “Shifts toward gender equality occur at uneven paces, with heterosexual marriage lagging behind other institutions.”

“As the range of acceptable roles and responsibilities continues to expand, men may become more comfortable with economic dependence,” she adds. If and when that occurs, they’ll presumably feel less of a need to establish their independence and/or masculinity by cheating on their wives.

Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.