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Table 15 Meta-analyses for number of cigarettes smoked a

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

Amount smoked Statisticb All lung cancerc Squamousd Adenoe
Number of setsf   190 48 46
About 5 cigs/dayg n 174 41 39
  F 3.25 (3.17-3.34) 6.07 (5.50-6.70) 2.70 (2.47-2.96)
  R 3.49 (3.13-3.89) 4.98 (3.93-6.31) 1.83 (1.40-2.39)
  H, PH 10.77, p < 0.001 3.85, p < 0.001 6.19, p < 0.001
About 20 cigs/dayh n 113 30 28
  F 5.30 (5.18-5.43) 12.36 (10.89-14.03) 3.58 (3.18-4.04)
  R 7.33 (6.29-8.54) 11.86 (8.92-15.76) 2.73 (2.06-3.61)
  H, PH 22.45, p < 0.001 3.72, p < 0.001 4.27, p < 0.001
About 45 cigs/dayi n 128 37 34
  F 10.17 (9.89-10.45) 28.95 (25.42-32.98) 7.20 (6.38-8.13)
  R 13.69 (11.80-15.89) 27.65 (20.42-37.44) 4.80 (3.29-7.01)
  H, PH 14.89, p < 0.001 3.98, p < 0.001 7.69, p < 0.001
  1. a Within each study, results are selected in the following preference order, within each sex, for:
  2. smoking status – ever, current;
  3. smoking product – any, cigarettes (ignoring other products), cigarettes only;
  4. cigarette type – any, manufactured (with or without handrolled), manufactured only;
  5. unexposed group – never any product, never cigarettes, near equivalent (see Methods);
  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. Results are by number of cigarettes or cigarette equivalents.
  15. 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).
  16. c All or nearest available, must include at least squamous cell carcinoma and adenocarcinoma.
  17. d Squamous cell carcinoma or nearest available, but not including adenocarcinoma.
  18. e Adenocarcinoma or nearest available, but not including squamous cell carcinoma.
  19. f Number of sets of RRs available for the key value analysis, where base for comparison is never smoked.
  20. g Category for which results are provided includes 5 cigs/day but does not include 20 cigs/day.
  21. h Category for which results are provided includes 20 cigs/day but does not include 5 or 45 cigs/day.
  22. i Category for which results are provided includes 45 cigs/day but does not include 20 cigs/day.