Smokers wanted.
D000368:Aged; D005069:Evaluation Studies as Topic; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000401:mortality; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D009316:National Institutes of Health (U.S.); D016032:Randomized Controlled Trials as Topic; D012307:Risk Factors; D012907:Smoking; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014481:United States