From: Meta-analysis of the relation between European and American smokeless tobacco and oral cancer
 | Unadjusted for any factor | Adjusted for smoking | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
 |  |  | Heterogeneityb |  |  |  | Heterogeneityb |  | ||
Factor | N | OR/RR (95%CI)a | χ2 | I2 | p(χ2)c | N | OR/RR (95%CI)a | χ2 | I2 | p(χ2)c |
All estimates d | 19 | 1.58 (1.39–1.78) | 232.1 | 92.2 | < 0.0001 | 15 | 1.31 (1.13–1.53) | 28.7 | 51.3 | 0.0114 |
Type | Â | Â | Â | Â | Â | Â | Â | Â | Â | Â |
Chewing tobacco | 3 | 3.20 (2.12–4.82) | 23.8 | 91.6 | < 0.0001 | 4 | 1.29 (0.99–1.69) | 5.6 | 46.2 | 0.1342 |
Snuff | 3 | 27.9 (17.0–45.9) | 19.6 | 89.8 | 0.0001 | 4 | 1.62 (1.24–2.11) | 13.4 | 77.7 | 0.0038 |
Smokeless e | 13 | 1.18 (1.03–1.35) | 31.5 | 61.9 | 0.0017 | 7 | 1.09 (0.85–1.42) | 5.4 | 0.0 | 0.4967 |
Between levels | Â | Â | 157.3 | 67.7 | < 0.0001 | Â | Â | 4.3 | 15.1 | 0.1142 |
Sex | Â | Â | Â | Â | Â | Â | Â | Â | Â | Â |
Female | 4 | 20.3 (12.6–32.5) | 35.0 | 91.4 | < 0.0001 | 2 | 2.51 (1.73–3.64) | 3.5 | 71.5 | 0.0610 |
Male | 7 | 1.27 (1.07–1.51) | 60.6 | 90.1 | < 0.0001 | 10 | 1.15 (0.97–1.37) | 10.8 | 16.4 | 0.2925 |
Both | 8 | 1.35 (1.11–1.64) | 16.5 | 57.5 | 0.0213 | 3 | 1.19 (0.66–2.15) | 0.6 | 0.0 | 0.7573 |
Between levels | Â | Â | 120.1 | 51.7 | < 0.0001 | Â | Â | 13.9 | 48.4 | 0.0010 |
Study design | Â | Â | Â | Â | Â | Â | Â | Â | Â | Â |
Case-control, hospital controls | 13 | 1.90 (1.64–2.21) | 200.4 | 94.0 | < 0.0001 | 7 | 1.41 (1.18–1.68) | 22.0 | 73.7 | 0.0009 |
Case-control, population controls | 6 | 1.01 (0.81–1.27) | 11.0 | 54.6 | 0.0514 | 3 | 0.99 (0.69–1.42) | 0.0 | 0.0 | 0.9935 |
Case-control, mixed controls | 0 | -- | -- | -- | -- | 2f | 1.35 (0.44–4.13) | -- | -- | 0.1337 |
Cohort | 0 | -- | -- | -- | -- | 3 | 1.24 (0.65–2.36) | -- | -- | 0.7062 |
Between levels | Â | Â | 20.7 | 8.9 | < 0.0001 | Â | Â | 3.0 | 10.4 | 0.3928 |
Study location | Â | Â | Â | Â | Â | Â | Â | Â | Â | Â |
USA | 15 | 1.76 (1.54–2.02) | 215.6 | 93.5 | < 0.0001 | 10 | 1.39 (1.17–1.64) | 23.7 | 62.1 | 0.0047 |
Scandinavia | 2 | 0.93 (0.67–1.30) | 1.1 | 5.3 | 0.3041 | 3 | 0.99 (0.68–1.45) | 0.2 | 0.0 | 0.9054 |
Other | 2g | 0.99 (0.53–1.84) | 1.3 | 24.6 | 0.2495 | 2h | 1.35 (0.44–4.13) | 2.2 | 55.5 | 0.1337 |
Between levels | Â | Â | 14.2 | 6.1 | 0.0008 | Â | Â | 2.5 | 8.8 | 0.2810 |
Study period | Â | Â | Â | Â | Â | Â | Â | Â | Â | Â |
-1969 | 5 | 4.49 (3.55–5.66) | 79.8 | 95.0 | < 0.0001 | 4 | 2.02 (1.28–3.20) | 3.6 | 15.8 | 0.3129 |
1970–1979 | 5 | 1.05 (0.84–1.33) | 33.0 | 87.9 | < 0.0001 | 1 | 2.67 (1.83–3.90) | 0.0 | 0.0 | -- |
1980–1989 | 7 | 1.01 (0.83–1.23) | 10.4 | 42.4 | 0.1080 | 2 | 0.97 (0.71–1.31) | 0.0 | 0.0 | 0.8743 |
1990+ | 2 | 1.37 (0.64–2.96) | 0.0 | 0.0 | 0.8321 | 8 | 1.10 (0.88–1.37) | 1.8 | 0.0 | 0.9719 |
Between levels | Â | Â | 108.9 | 46.9 | < 0.0001 | Â | Â | 23.4 | 81.4 | < 0.0001 |