Epidemiology of smoking

A team of British scientists headed by Richard Doll carried out a longitudinal study of 34,439 medical specialists from 1951 to 2001, generally called the "British doctors study". The study demonstrated that smoking decreased life expectancy by 10 years and that almost half of the smokers died from smoking (cancer, heart disease, and stroke). About 5,900 of the study participants are still alive and only 134 of them still smoke.

See bmjjournals for the study.