PLCO administered two questionnaires which queried about health and lifestyle factors, including smoking and lung disease. The first questionnaire was administered at PLCO baseline, between 1993–2001, with the date of administration dependent upon a participant’s date of randomization. The second questionnaire was administered during PLCO follow-up in 2006 to all participants; average duration between PLCO baseline and follow-up questionnaire was 8.7 (SD 1.8) years.
