Sub-group types | Studies n | Heterogeneity | OR (95% CI) | p-value | |
I2 % | p-value | ||||
Exposure to biomass smoke# | |||||
Sex | |||||
Female | 5 | 0.0 | 0.434 | 1.98 (1.44–2.73) | 0.881¶ |
Male | 1 | NA | NA | 1.78 (0.46–6.93) | |
Male and female | 2 | 0.0 | 0.404 | 1.20 (1.03–1.39) | |
Cancer histological sub-type | |||||
Unspecified | 6 | 15.8 | 0.309 | 1.31 (1.09–1.58) | |
Adenocarcinoma | 1 | NA | NA | 3.30 (1.36–8.00) | 0.942+ |
Squamous carcinoma | 1 | NA | NA | 3.50 (0.95–12.90) | |
Adjustment for smoking | |||||
Yes | 3 | 44.1 | 0.111 | 1.36 (0.99–1.86) | 0.183 |
Non-smokers only | 4 | 0.0 | 0.814 | 1.89 (1.31–2.73) | |
Study design | |||||
Population based | 1 | NA | NA | 1.11 (0.44–2.80) | 0.327 |
Hospital based | 5 | 54.3 | 0.053 | 1.84 (1.23–2.76) | |
Sample size | |||||
>368 | 5 | 55.6 | 0.061 | 1.45 (1.10–1.91) | 0.485 |
≤368 | 3 | 10.8 | 0.339 | 1.88 (0.96–3.70) | |
Language of publication | |||||
Chinese | 0 | NA | NA | NA | |
English | 9 | 41.2 | 0.092 | 1.50 (1.17–1.94) | |
Newcastle-Ottawa score | |||||
>6 | 7 | 43.0 | 0.104 | 1.42 (1.04–1.94) | 0.326 |
≤6 | 2 | 0.0 | 0.860 | 1.82 (1.24–2.68) | |
Quality of exposure assessment | |||||
1 star | 1 | NA | NA | 1.90 (1.03–3.50) | |
2 stars | 7 | 43.9 | 0.098 | 1.42 (1.07–1.87) | |
3 stars | 1 | NA | NA | 2.70 (0.82–8.90) | |
Exposure to coal smoke# | |||||
Sex | |||||
Female | 10 | 45.5 | 0.043 | 1.70 (1.40–2.06) | 0.490¶ |
Male | 3 | 26.0 | 0.259 | 1.54 (1.25–1.88) | |
Male and female | 12 | 39.9 | 0.068 | 2.19 (1.74–2.76) | |
Cancer histological sub-type | |||||
Unspecified | 16 | 38.1 | 0.047 | 1.70 (1.51–1.92) | |
Adenocarcinoma | 4 | 0.0 | 0.501 | 2.22 (1.60–3.08) | 0.324+ |
Squamous carcinoma | 5 | 61.2 | 0.035 | 3.81 (1.37–10.58) | |
Adjustment for smoking | |||||
Yes | 19 | 33.4 | 0.054 | 1.82 (1.62–2.06) | 0.909 |
Non-smokers only | 3 | 76.7 | 0.014 | 1.73 (0.73–4.10) | |
Study design | |||||
Population based | 13 | 60.4 | 0.001 | 1.89 (1.59–2.25) | 0.730 |
Hospital based | 9 | 43.4 | 0.008 | 1.82 (1.60–2.06) | |
Sample size | |||||
>368 | 13 | 36.0 | 0.087 | 2.04 (1.59–2.61) | 0.246 |
≤368 | 11 | 49.3 | 0.019 | 1.72 (1.49–2.00) | |
Language of publication | |||||
Chinese | 8 | 0.0 | 0.468 | 2.16 (1.81–2.59) | 0.022 |
English | 20 | 42.3 | 0.024 | 1.65 (1.43–1.91) | |
Newcastle-Ottawa score | |||||
>6 | 20 | 42.3 | 0.024 | 1.65 (1.43–1.91) | 0.022 |
≤6 | 8 | 0.0 | 0.468 | 2.16(1.81–2.59) | |
Quality of exposure assessment | |||||
1 star | 7 | 0.0 | 0.584 | 2.11 (1.75–2.56) | |
2 stars | 18 | 53.8 | 0.004 | 1.72 (1.47–2.02) | |
3 stars | 3 | 0.0 | 0.765 | 1.50 (0.71–3.20) |
NA: not available. #: the total number of biomass studies is seven but as some studies reported more than one sub-group the number of studies do not add up to seven in all sub-group types; similarly, the total number of coal studies is 22; ¶: females versus males; +: adenocarcinoma versus squamous carcinoma.