For instance, one of the most commonly cited statistics about marriage is that half of marriages end in divorce. But that number reflects the expected lifetime divorce rate of people married in the 1970s.

The story is different for more-recently married couples. A comparison of 10-year divorce rates among college-educated men married in the 1970s, 1980s and 1990s shows that divorce is becoming less common, said Dr. Stevenson, the Wharton researcher. Among men who married in the 1970s, for example, about 23 percent had divorced by the 10th year of marriage. Among similar men married in the 1980s, about 20 percent had divorced by the 10th year. Men married in the 1990s are doing even better — with a 10-year divorce rate of 16 percent…

The reason for these shifts, some experts say, is that many couples today are delaying marriage. And age matters. People who marry after age 25 are less likely to divorce than those who marry earlier, studies find. Men and women born in the 1930s who married in the 1950s have the highest marriage rate of any generation — about 96 percent married. But among more recent generations, the number has dropped to about 90 percent. The data suggest that the weakest relationships, which years ago might have resulted in a marriage followed by a divorce, are now ending before the couple ever heads to the altar.