Smokers who are paid to quit succeed far more often than those who get no cash reward, according to a new study that provides some of the strongest evidence yet that financial incentives can help change such behavior.

The study, one of the largest of its kind, comes at a time when more employers, schools and other institutions are paying people to do everything from lose weight to improve their grades. The latest findings were published in this week's New England Journal of Medicine.

Smoking...