In 2012, 57 percent of Americans believed it is alright for a couple to live together without intending to get married.

The dominance of marriage may be due to a cultural lag, where attitudes and values change more slowly than the primary material conditions.

• In 1997, the median age for a first marriage was 27.4 for women and 29.5 for men.
• The college-educated are more likely to marry eventually. Nine out of ten wait until after they marry to have children.
• A large portion of those without college educations have a child before...