TTFC information was collected on the PLCO follow-up questionnaire in 2006; since TTFC reflects current smoking habits, only current smokers were queried about TTFC. The question was “How soon after you wake up do you usually smoke your first cigarette of the day?” Participants selected their response from the following four categories: within 5, 6–30, 30–60, or >60 minutes of waking.
