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Table 13 Meta-analyses for smoking of cigarettes, cigars and pipes (all lung cancer) a

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

Product smoked Statisticb Ever smoking Current smoking Ex smoking
Cigarettes only n 53c 35c 21
  F 4.37 (4.27-4.47) 9.32 (8.87-9.80) 4.36 (4.05-4.69)
  R 6.36 (5.33-7.59) 9.57 (7.90-11.59) 4.22 (3.29-5.40)
  H, PH 22.95, p < 0.001 10.91, p < 0.001 7.96, p < 0.001
Pipes/cigars only n 38 26 7
  F 3.46 (3.20-3.73) 3.74 (3.29-4.26) 2.00 (1.50-2.65)
  R 2.92 (2.38-3.57) 4.76 (3.44-6.59) 2.00 (1.50-2.65)
  H, PH 3.60, p < 0.001 4.18, p < 0.001 0.46, NS
Pipes only n 23 12 5
  F 3.36 (2.95-3.81) 5.28 (4.55-6.13) 3.32 (2.42-4.55)
  R 3.31 (2.51-4.35) 5.20 (3.50-7.73) 2.69 (1.53-4.72)
  H, PH 3.49, p < 0.001 5.43, p < 0.001 2.66, p < 0.05
Cigars only n 15 15 5
  F 2.73 (2.32-3.21) 4.05 (3.61-4.54) 3.27 (2.36-4.52)
  R 2.95 (1.91-4.56) 4.67 (3.49-6.25) 2.85 (1.45-5.61)
  H, PH 5.68, p < 0.001 4.27, p < 0.001 4.11, p < 0.01
Mixed n 27 9 7
  F 7.87 (7.22-8.59) 9.63 (8.46-10.96) 4.79 (4.10-5.60)
  R 7.37 (5.97-9.11) 9.60 (8.37-11.00) 5.51 (3.88-7.82)
  H, PH 4.09, p < 0.001 1.05, NS 3.72, p < 0.01
  1. a Within each study, results for the relevant smoking product and smoking status are selected in the following preference order, within each sex, for:
  2. unexposed group – never any product, near equivalent (see Methods);
  3. follow-up period – longest available;
  4. lung cancer type – all or nearest available, must include at least squamous cell carcinoma and adenocarcinoma;
  5. race – all or nearest available, otherwise by race;
  6. overlapping studies – principal, subsidiary;
  7. age – whole study, widest available age group;
  8. sex – single sex results, combined sex results;
  9. adjustment for potential confounders – most available.
  10. 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), PB = probability value for between levels (see Methods) similarly expressed.
  11. c Results differ from those shown earlier (Tables 6, 9) because RRs with unexposed group “never cigarettes” are excluded here.