Even if the odds are stacked against you, marriage can more than compensate. Linda Waite of the University of Chicago has found that a married older man with heart disease can expect to live nearly four years longer than an unmarried man with a healthy heart. Likewise, a married man who smokes more than a pack a day is likely to live as long as a divorced man who doesn't smoke. There's a ‍ flip side , however, as partners are more likely to become ill or die in the couple of years following their spouse’s death, and caring for a spouse with mental disorder can leave you with some of the same severe problems. Even so, the odds favor marriage. In a 30-year study of more than 10,000 people, Nicholas Christakis of Harvard Medical School describes how all kinds of social networks have similar effects.