Will it last? Photographer: Joe Raedle/Getty Images
Will it last? Photographer: Joe Raedle/Getty Images

Can a mathematical formula predict the length of your relationship? As much as this might sound like useless clickbait, there is some qualitative sense to a formula that the MSN Internet portal has hit upon.

Using data from a survey of 2,000 men and women, MSN created a formula encompassing 10 inputs. They include the importance that partners attach to good looks, children, in-laws, honesty and money. Most of the inputs were rated on a scale of 1 to 5, limiting their impact on the overall score. As a result, only two inputs could have an outsize effect: the number of years the partners knew each other before they became serious and the number of previous sexual partners. The latter one is especially important. Playing with the formula, I found that a total of about 180 previous partners for the couple should make any relationship a nonstarter, even if all other circumstances are ideal.

Is the number of previous partners really such an important element of a relationship? Actually, research suggests it is.

Back in 1977, with the sexual revolution in full swing, UCLA's Letitia Anne Peplau and her collaborators established that "women reported significantly more love for a man if he was their first sexual partner. Similarly, men reported greater love for a woman who lost their virginity with him than with a previous partner." People of both genders also thought the probability of marriage was greater if the man was the woman's first sexual partner.

That did not change much in the next quarter-century. In 2003, Jay Teachman of Western Washington University published an article establishing a strong relationship between the variety of a woman's premarital sexual experience and the likelihood that her marriage would break up. "Women with more than one intimate relationship prior to marriage have an elevated risk of marital disruption," Teachman wrote. "The risk of divorce is particularly great for women who cohabited with both their husbands and another man." Having at least one sexual relationship before marriage, Teachman found, increased the probability of divorce 53 percent.

Relationships have changed a lot since the 1990s, the period from which Teachman drew his data. Recent studies show that living together before marrying no longer increases the probability of divorce. Still, according to a Bowling Green State University study based on statistics from 2006 to 2008, women who had no sexual partners other than their husbands and who started living with their spouse only after marriage had the smallest risk of breakup.

One possible explanation can be found in a paper published last year, in which researchers found a strong positive relationship between the number of sexual partners and subsequent substance abuse. Even if formerly promiscuous people remain loyal to their spouses, their marriages can still fail if they start drinking heavily or get hooked on drugs.

We may think, based on our own experiences, that conservative notions of abstinence are obsolete and no longer relevant. MSN's survey, no matter how unscientific, offers further evidence to the contrary. People are uncomfortable with their partners' rich sexual histories. A quarter of the men and women MSN surveyed believed their partner should have had just four previous partners, and 21 percent of the men want to be their ideal woman's first. According to the Bowling Green study, 12.3 percent of women who married between 1996 and 2006 were virgins up until the wedding.

There is, of course, no universal recipe for a lasting relationship. According to MSN's formula, my marriage should have had a negative duration. My wife and I have been together for 10 years now. But if you're mathematically inclined and probabilities matter to you, abstinence and extreme selectivity are good bets.

(Leonid Bershidsky writes on Russia, Europe and technology for Bloomberg View. Follow him on Twitter at @Bershidsky.)

To contact the writer of this article: Leonid Bershidsky at lbershidsky@bloomberg.net.

To contact the editor responsible for this article: Mark Whitehouse at mwhitehouse1@bloomberg.net.