Skip to main content

Table 19 Meta-analyses for duration of quitting (vs. current smoking) a

From: Systematic review with meta-analysis of the epidemiological evidence in the 1900s relating smoking to lung cancer

Duration of quitting Statisticb All lung cancerc Squamousd Adenoe
Number of setsf   58 11 11
About 3 yearsg n 41 6 6
  F 0.98 (0.93-1.04) 1.15 (1.03-1.28) 1.02 (0.85-1.22)
  R 0.95 (0.84-1.08) 1.15 (1.03-1.28) 1.02 (0.85-1.22)
  H, PH 3.55 p < 0.001 0.51, NS 0.74, NS
About 7 yearsh n 29 4 4
  F 0.60 (0.56-0.64) 0.74 (0.65-0.85) 0.73 (0.58-0.92)
  R 0.57 (0.50-0.64) 0.74 (0.65-0.85) 0.73 (0.58-0.92)
  H, PH 2.09, p < 0.001 0.09, NS 0.59, NS
About 12 yearsi n 48 9 9
  F 0.32 (0.30-0.34) 0.40 (0.35-0.47) 0.50 (0.41-0.60)
  R 0.28 (0.24-0.32) 0.27 (0.18-0.40) 0.39 (0.26-0.58)
  H, PH 4.22, p < 0.001 4.07, p < 0.001 3.68, p < 0.001
Longest vs. shortestj n 61 12 12
  F 0.23 (0.21-0.25) 0.19 (0.16-0.22) 0.30 (0.23-0.37)
  R 0.24 (0.20-0.29) 0.14 (0.08-0.25) 0.21 (0.10-0.46)
  H, PH 5.21, p < 0.001 6.68 p < 0.001 9.44, p < 0.001
  1. a Within each study, results for ex smokers are selected in the following preference order, within each sex, for:
  2. smoking product – any, cigarettes (ignoring other products), cigarettes only;
  3. cigarette type – any, manufactured (with or without handrolled), manufactured only;
  4. adjustment for other aspects of smoking – least available;
  5. comparison group – current smokers, current and recent smokers (up to 2 years);
  6. follow-up period – longest available;
  7. lung cancer type – see notes c to e;
  8. race – all or nearest available, otherwise by race;
  9. overlapping studies – principal, subsidiary;
  10. age – whole study, widest available age group;
  11. Results are then selected for:
  12. sex –- single sex results, combined sex results;
  13. adjustment for potential confounders – most available.
  14. b n = number of estimates combined, F = fixed-effect meta-analysis RR (95% CI), R = random-effects meta-analysis RR (95% CI), H = heterogeneity chisquared per degree of freedom, PH = probability value for heterogeneity expressed as p < 0.001, p < 0.05, p < 0.1 or NS (p ≥ 0.1).
  15. c All or nearest available, must include at least squamous cell carcinoma and adenocarcinoma.
  16. d Squamous cell carcinoma or nearest available, but not including adenocarcinoma.
  17. e Adenocarcinoma or nearest available, but not including squamous cell carcinoma.
  18. f Number of sets of RRs available for the key value analysis, where base for comparison is never smoked.
  19. g Category for which results are provided includes 3 years but does not include 7 years.
  20. h Category for which results are provided includes 7 years but does not include 3 or 12 years.
  21. i Category for which results are provided includes 12 years but does not include 7 years.
  22. j For this analysis only, the exposed and unexposed group have the same smoking status (i.e. ex-smokers), product and cigarette type. There is a preference (instead of that for comparison group) to select the results for the longest (=exposed) and shortest (=unexposed) duration quitters. Note that (unlike the inverse results shown in Table 18), the “shortest” quitters here may omit recent quitters, but subject to a limit of no more than two years.