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Table 4 Meta-analyses of the risk of oral cancer in smokeless tobacco users compared to non-users (based on the estimates given in Table 3).

From: Meta-analysis of the relation between European and American smokeless tobacco and oral cancer

      Heterogeneity  
Type of smokeless tobacco No. of estimates combined Adjustment factorsa Fixed-effect
OR/RR (95%CI)
Random-effects
OR/RR (95%CI)
χ2 I2 p(χ2)
Allb 38 any 1.54 (1.40–1.69) 1.87 (1.40–2.48) 283.3 86.9 < 0.0001
  19 none 1.58 (1.39–1.78) 2.18 (1.35–3.53) 232.1 92.2 < 0.0001
  15 sm 1.31 (1.13–1.53) 1.35 (1.04–1.76) 28.7 51.3 0.0114
  7 sm, al 1.02 (0.82–1.28)   1.9 0.0 0.9321
  7 sm, al, age 1.02 (0.82–1.28)   1.9 0.0 0.9321
Chewing 14 any 1.38 (1.21–1.58) 1.36 (0.98–1.89) 61.2 78.8 < 0.0001
  8 none 1.37 (1.13–1.68) 1.28 (0.71–2.30) 46.4 84.9 < 0.0001
  6 sm 1.39 (1.16–1.66) 1.42 (0.99–2.03) 14.9 66.3 0.0110
  1 sm, al, age 1.00 (0.71–1.41)   -- -- --
Snuff 15 any 2.00 (1.67–2.39) 2.39 (1.17–4.89) 182.4 92.3 < 0.0001
  7 none 5.36 (3.73–7.69) 5.15 (0.88–30.2) 116.7 94.9 < 0.0001
  7 sm 1.35 (1.09–1.69) 1.28 (0.76–2.14) 24.8 75.8 0.0004
  3 sm, al 0.88 (0.65–1.18)   0.4 0.0 0.7998
  2 sm, al, age 0.93 (0.64–1.36)   0.2 0.0 0.6555
Smokelessc 24 any 1.27 (1.13–1.42) 1.46 (1.17–1.83) 65.6 65.0 < 0.0001
  13 none 1.18 (1.03–1.35) 1.26 (0.98–1.61) 31.5 61.9 0.0017
  7 sm 1.09 (0.85–1.42)   5.4 0.0 0.4967
  6 sm, al, age 1.04 (0.80–1.35)   1.8 0.0 0.8751
  4 sm, al, age, ss 1.32 (0.77–2.25)   0.8 0.0 0.8467
  1. a Smoking (sm), alcohol (al), age, social status (ss)
  2. b For each study/sex, the OR/RR for smokeless tobacco from Table 3 was included if available, otherwise that for chewing tobacco or snuff was used. For study 25 where estimates for snuff and chewing tobacco, but not smokeless tobacco, were available, that for chewing tobacco was included as it was for smokers and nonsmokers combined
  3. c This includes all the OR/RR estimates from Table 3 where the exposure was smokeless, both from studies where only estimates for unspecified exposure were available and from studies where it had been estimated from the separate data for chewing tobacco and snuff