Table 2.
Subgroup analyses of the lung cancer risk associated with household coal use for heating and cooking in mainland China and Taiwan
| Subgroups within mainland China and Taiwan | Number of studies | Heterogeneity [I2 (%); P-value] | OR (95% CI) |
|---|---|---|---|
| Gender | |||
| Female | 8 | 80.9; 5.3 × 10−6 | 2.50 (1.56–4.00) |
| Male | 3 | 82.4; 0.003 | 2.76 (1.44–5.27) |
| Non-smoking females | 3 | 0.0; 0.433 | 2.93 (1.40–6.12) |
| Non-smoking males | 0 | Not applicable | Not applicable |
| Geographical setting | |||
| Only studies carried out in an urban setting | 9 | 92.8; 1.6 × 10−22 | 2.35 (1.44–3.84) |
| Only studies carried out in a rural setting | 3 | 83.4; 0.002 | 3.28 (1.46–7.39) |
| Type of questionnaire used to assess coal exposuresa | |||
| Only studies utilizing a qualitative question to assess coal exposure | 13 | 92.5; 7.9 × 10−28 | 2.16 (1.43–3.26) |
| Only studies utilizing a quantitative question to assess coal exposure | 7 | 81.5; 1.4 × 10−5 | 2.49 (1.47–4.20) |
| Publication language | |||
| Only studies published in English | 11 | 94.7; 3.9 × 10−35 | 2.36 (1.42–3.94) |
| Only studies published in Chinese | 9 | 0.0; 0.87 | 2.01 (1.69–2.40) |
| Sample size of study | |||
| Only studies with greater than 800 subjects | 6 | 87.5; 1.5 × 10−7 | 2.27 (1.43–3.59) |
| Only studies with less than 800 subjects | 14 | 88.5; 4.2 × 10−18 | 2.24 (1.51–3.32) |
| Study design | |||
| Only population-based case–control studies | 13 | 93.2; 1.8 × 10−31 | 2.57 (1.64–4.03) |
| Only hospital-based case–control studies | 6 | 0.0; 0.89 | 1.75 (1.47–2.09) |
aAll studies assessed exposure using a questionnaire. The questions used were classified into qualitative (i.e. questions with yes/no responses, such as do you burn coal at home?) and quantitative (i.e. number of years of exposure or amount of coal use).