• Women who never smoked;
• Women who smoked and quit before diagnosis;
• Women who smoked and quit after diagnosis;
• Women who continued to smoke after diagnosis.
Participants were asked to report on such factors as whether they had smoked at least 100 cigarettes during their lifetime, their age when they started smoking, and the average number of cigarettes they smoked a day. The authors controlled for several important risk factors that could impact survival, including alcohol consumption and body mass index.