Researchers in Australia may have figured out what it takes to keep a couple together…and it’s a lot more than just being in love.

A couple’s age, previous relationships, even whether they smoke or not, all have an influence on whether or not their marriage will last, according to a recent Australian study on marriage longevity.

The study, called “What’s Love Got to Do With It?” followed over 2,000 couples who were either married or living together, for six years from 2001 to 2007, to identify factors associated with those who stayed together, compared with those who divorced or separated.

Among the things they discovered: a husband who is nine or more years older than his wife is twice as likely to get a divorce. This also applies to husbands who marry before age 25.

Children definitely influence the longevity of a marriage. One-fifth of couples who have kids before marriage — either from a previous relationship, or in the same relationship — end up separating, compared to just 9% of those couples who have no children until after they marry.

Women who want children significantly more than their partners are also more likely to divorce.

The in-laws also have a role to play in a couple’s relationship. The study showed that 16% of men and women whose parents separated or divorced experienced marital difficulties themselves, compared to just 10% for couples whose parents stayed together, happily or not.

Couples in which one or both spouses are on their second or third marriage are 90% more likely to separate than couples who are both in their first marriage.

Not surprisingly, money also has an effect. Up to 16% of those who indicated they were poor, or that the husband (but not the wife) was unemployed, separated, compared with only 9% of couples in relatively good financial shape.

Surprisingly, couples in which only one partner is a smoker are also more likely to have the relationship end in failure.

The factors that the study found do not significantly increase separation risk included: the number and age of children born to a married couple, the wife’s employment status and the number of years the couple had been employed.

The study was jointly written by researchers from The Australian National University, and the Department of Families, Housing, Community Services and Indigenous Affairs.