title: How rapidly does the excess risk of lung cancer decline following quitting smoking? A quantitative review using the negative exponential model.
abstract: The excess lung cancer risk from smoking declines with time quit, but the shape of the decline has never been precisely modelled, or meta-analyzed. From a database of studies of at least 100 cases, we extracted 106 blocks of RRs (from 85 studies) comparing current smokers, former smokers (by time quit) and never smokers. Corresponding pseudo-numbers of cases and controls (or at-risk) formed the data for fitting the negative exponential model. We estimated the half-life (H, time in years when the excess risk becomes half that for a continuing smoker) for each block, investigated model fit, and studied heterogeneity in H. We also conducted sensitivity analyses allowing for reverse causation, either ignoring short-term quitters (S1) or considering them smokers (S2). Model fit was poor ignoring reverse causation, but much improved for both sensitivity analyses. Estimates of H were similar for all three analyses. For the best-fitting analysis (S1), H was 9.93 (95% CI 9.31-10.60), but varied by sex (females 7.92, males 10.71), and age (<50years 6.98, 70+years 12.99). Given that reverse causation is taken account of, the model adequately describes the decline in excess risk. However, estimates of H may be biased by factors including misclassification of smoking status.
authors.affiliation: P N Lee Statistics and Computing Ltd., Sutton, Surrey, United Kingdom.
authors.forename: John S
authors.initials: JS
authors.lastname: Fry
authors.forename: Peter N
authors.initials: PN
authors.lastname: Lee
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Forey
authors.forename: Katharine J
authors.initials: KJ
authors.lastname: Coombs
mesh_terms: D000368:Aged; D005260:Female; D006207:Half-Life; D006801:Humans; D008175:Lung Neoplasms / Q000209:etiology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D012306:Risk; D012907:Smoking / Q000009:adverse effects*; D016540:Smoking Cessation; D014029:Tobacco Use Disorder / Q000473:pathology* / Q000517:prevention & control
keywords: Cessation of smoking; Lung cancer; Meta-analysis; Negative exponential model; Review; Smoking; Statistical models