Most unmarried couples who live together aren’t trying to test their relationship, according to a new US study of dating and cohabitation.

The finding seems to contradict the popular view of cohabitation as a trial marriage. Only one in ten cohabiting couples see their relationship in these terms. It is one of the early results from the study, scheduled to continue for years, and it gives researchers new insight into the burgeoning number of couples who cohabit.

Cohabitation has increased so rapidly that the data about it haven’t kept pace with the growing numbers, researchers say. The latest U.S. Census for 2008 reported 13.6 million unmarried, heterosexual couples living together. According to Census 2006, the number of Irish couples cohabiting is now over 120,000, a four-fold increase in just ten years.

Researchers say 50 per cent to 60 per cent of couples who marry today lived together first; some note that 70 per cent of young adults will cohabit. Most couples who live together either marry or break up within two years.

This first snapshot of the new federally funded study of 1,294 unmarried Americans ages 18 to 34 was presented last week at a convention of marriage and family experts in Orlando. Those who study cohabitation say it will provide good documentation for years on how such relationships evolve and on the changing role of cohabitation.

“People who are engaged think of (living together) as the next step before they get married, but in many couples, it’s part of the dating relationship – pretty serious, but still well shy of the marriage part,” says researcher Scott Stanley, co-director of the Center for Marital and Family Studies at the University of Denver.

Almost half of cohabitors of both sexes in the study cite spending more time together as a reason they moved in together; just nine per cent of men and five per cent of women cited “to test the relationship before marriage.”

“National surveys show many young people believe cohabitation is a good way to test a relationship,” says co-researcher Galena Rhoades, also of the University of Denver. “So it’s surprising that very few individuals identify ‘testing the relationship’ as their primary reason.”

The study also found that most couples didn’t consciously decide to live together; two-thirds of cohabitors said they either “slid into it” or “talked about it, but then it just sort of happened.” Just one-third talked about it and made a decision to live together.

Perhaps unsurprisingly, the report showed that the more religious were less likely to cohabit: 49 per cent of dating couples and 30 per cent of cohabitors surveyed agree that “my religious beliefs suggest that it is wrong for people to live together without being married.”

Participants complete questionnaires two to three times a year; more than 100 questions are in each survey. More than two-thirds are in a serious dating relationship; 32 per cent live together.

Of those cohabiting, 66 per cent moved in before making plans to marry; 23 per cent planned to marry but weren’t engaged, and 11 per cent moved in when they got engaged.

Another study, the National Longitudinal Study of Adolescent Health, illustrates the difficulties of studying cohabitation. The 1,733-question survey asked two questions related to cohabitation; data are from 2001-02. Those findings are part of an analysis released last week by the non-profit Child Trends, which examined statistics on 11,998 young adults ages 20-24.

It finds most young people view cohabitation positively and see living together as a temporary alternative to marriage. Most say they hope to marry someday.

Other research by the same researchers, published this year, reinforces previous findings about cohabitation and is similar to the new Denver study.

A survey of 1,050 people who were married less than 10 years published in the Journal of Family Psychology suggests cohabiting before engagement is associated with lower marital satisfaction. A study of 120 cohabiting couples in the Journal of Family Issues also found unmarried partners cohabit to spend more time together, not to test the relationship.