Smoking status at baseline is measured with smoking-related data gathered at the baseline interview. Current and former smoking habits are assessed using the following questions:

1. Do you smoke cigarettes now?
2. Did you ever smoke cigarettes regularly?

Question 1 is used to determine current smokers, and question 2 identifies previous smokers. Participants who answer "no" to both questions are categorized as "never smoked" (see below).

Note: Categories are mutually exclusive.