Table 6.
Effect estimates for never smokersa
| Study | First author, year of publication | Adjustment factors | Exposure | Sex | Exposed cases | OR/RR (95%CI) |
| Studies providing result specific for oral cancer | ||||||
| 8 | Keller 1970 [75] |
None | Smokeless | M | 4 | 3.04 (0.62–14.99) |
| 16 | Blot 1988 [100] |
Age, race, location, respondent | Smokeless | F | 6 | 6.20 (1.90–19.80) |
| 19 | Blomqvist 1991 [103] |
None | Snuff | M+F | 2 | 0.67 (0.08–5.75) |
| 25 | Kabat 1994 [59] |
None | Smokeless | M | 4 | 1.59 (0.51–4.96) |
| F | 4 | 38.7 (2.1–723.6)b | ||||
| 29 | Schildt 1998 [73] |
Age, sex, residence | Snuff | M+F | 19 | 0.70 (0.40–1.20) |
| 32 | Henley 2005 [66] |
Age, race, education, alcohol, exercise, aspirin, body mass index, diet, occupationc | Smokeless | M (CPS-I) | 4 | 2.02 (0.53–7.74) |
| M (CPS-II) | 1 | 0.90 (0.12–6.71) | ||||
| Fixed-effect meta-analysis estimate for six studies | 1.30 (0.87–1.93) | |||||
| Random-effects meta-analysis estimate for six studies | 1.94 (0.88–4.28) | |||||
| Heterogeneity | χ2 (df) | 18.99 (7) | ||||
| p | 0.0082 | |||||
| I2 | 63.13 | |||||
| Additional study providing result for oral, larynx and oesophagus cancer combined | ||||||
| 27 | Lewin 1998 [64] |
Age, region | Snuff | M | 9 | 4.70 (1.60–13.80) |
| Fixed-effect meta-analysis estimate for all seven studies | 1.51 (1.04–2.19) | |||||
| Random-effect meta-analysis estimate for all seven studies | 2.20 (1.04–4.67) | |||||
| Heterogeneity | χ2 (df) | 23.82 (8) | ||||
| p | 0.0025 | |||||
| I2 | 66.42 | |||||
aSee the discussion section for the reasons why data from study 15 [65] were not included in Table 6
b There were no exposed controls and the OR was estimated by adding 0.5 to each cell in the 2 × 2 table
cOccupation only adjusted for in CPS-II