The divorce rate in the United States is declining, according to a study conducted by researchers at Rutgers University. But one reason may be found in another statistic from the study: the number of Americans choosing to get married in the first place has been going down.

The American divorce rate today is nearly twice what it was in 1960. The often-quoted statistic is that 50% of all American marriages will end in divorce. But since hitting a high point in the early 1980s, the divorce rate in this country has actually been going down, according to David Popenoe, a sociology professor who directs the National Marriage Project at Rutgers University. "Probably the biggest reason is that people are marrying at a later age," he says. "This means, essentially, that you have fewer teen marriages, and teen marriages have by far the highest divorce rate."

Today, the average American man is 27 years old when he gets married for the first time. Compare that to 30 years ago, when the average was just 23. Most American women these days are around 25 years old when they finally walk down the aisle. But in 1970, the average was 20.

David Popenoe says Americans are postponing marriage so they can continue their educations and get started on their careers. That does not mean, though, that they are putting personal relationships on hold. "If you postpone marriage for a long time," Professor Popenoe says, "The question becomes what do you do in the meantime? And co-habitation is quickly filling the bill."

"Co-habitation." It is a term that refers to the increasingly common practice in which a man and woman who are romantically involved with one another - but are not married - live together as if they are. Between 1960 and 2004, the number of co-habiting couples in the United States increased by nearly 1200% percent. About 9% of the men and women living together today are not married. Although that rate pales in comparison to some European countries -- where the rate can be as high as60% -- it is still higher now than it has ever been before.

Many co-habiting couples do eventually marry, but not all of them. Mary Bayless, for example, who resides in a suburb of Washington, D.C., says she probably will not ever marry the man she has been living with for the past 3 years. "When we first started seeing each other, we were both going through divorces," she recalls. "He wanted to get married, I didn't. And then after we both divorced and [were] living together, I started talking about marriage, and he didn't want anything to do with it. And now we're both kind of at the same impasse, that we just don't want to get married." Ms. Bayless notes that the decision is not a reflection of their feelings for one another, so much as it is a reflection of their attitudes toward marriage.

Many of the couples who live together have experienced divorce on some level. Either they have been divorced themselves, or else their parents separated. Professor David Popenoe says the co-habitation rate is particularly high among people who were children in the late 1970s and early 1980s, when the U.S. divorce rate reached its peak. "We're finding now that people - especially those who come from broken homes, through divorce and so on - are gun-shy [i.e. afraid] of marriage," he says. "They want to make sure they've found just the right person, and they're in no rush to have to go through a divorce themselves."

David Popenoe says co-habitation has become so commonplace, that there is very little pressure these days for people to marry. But Mary Bayless says researchers should not be fooled by the high co-habitation rates. She says there is still a lot of subtle pressure to marry. "I'm 50 years old, he's 47. I hate introducing him or talking about him as my 'boyfriend,'" she says. "It sounds so 'high school.' And I hate all the other terms, you know, 'partner,' 'companion.' It sounds like I'm gay! I just don't know what the right term is for him, so that's part of it."

Mary Bayless says she believes American society is more accepting of co-habitation among young adults, because the assumption is that these people will eventually get married. That may be the case, but many young, co-habiting couples may be facing a different kind of social judgment. According to the National Marriage Project, more than 40% of them have children - and polls show that about 1/2 of all Americans believe they should have exchanged wedding vows before starting a family.