When the price of a pack of cigarettes increases by $1, there is a 20 percent increase in rates of quitting smoking.

Researchers linked data on the smoking habits of 632 smokers, average age 58, to neighborhood cigarette prices in 896 chain grocery and drugstores in 19 states. They gathered data on local laws on indoor smoking in public places, and followed changes in prices, laws and smoking habits over 10 years.

The study, in Epidemiology, found that a $1 increase in price was linked to a 7 percent reduction in the risk of heavy smoking (10 cigarettes or more a day), and a 35 percent reduction in the average number of cigarettes smoked by heavy smokers.

At the same time, they found no effect of price on smoking relapse, and local smoking bans had little impact on any of their estimates.