Table 2.
Results of meta-analysis for cigarette smoking and risk of glioma
| Group | No of studies | RR (95% CI) | P-value | I2 (%) | P-heterogeneity | Analysis model |
|---|---|---|---|---|---|---|
| Total | 24 | 1.04 (1.00, 1.09) | 0.072 | 28.6 | 0.096 | Fixed-effects model |
| Study design | ||||||
| Cohort | 7 | 1.05 (0.97, 1.13) | 0.200 | 32.7 | 0.178 | Fixed-effects model |
| Case–control | 17 | 1.04 (0.98, 1.10) | 0.201 | 31.2 | 0.107 | Fixed-effects model |
| Hospital-based | 8 | 0.98 (0.87, 1.11) | 0.773 | 0.0 | 0.423 | Fixed-effects model |
| Population-based | 9 | 1.06 (0.99, 1.13) | 0.106 | 43.1 | 0.080 | Fixed-effects model |
| Research instrument (cohort) | ||||||
| Mailed questionnaire | 4 | 1.08 (0.98, 1.19) | 0.105 | 0.0 | 0.633 | Fixed-effects model |
| Self-admin questionnaire | 3 | 1.14 (0.84, 1.54) | 0.403 | 67.9 | 0.045 | Random-effects model |
| Research instrument (case–control) | ||||||
| Interview | 11 | 1.05 (0.98, 1.12) | 0.142 | 36.3 | 0.118 | Fixed-effects model |
| Questionnaires | 3 | 1.00 (0.84, 1.19) | 0.972 | 35.1 | 0.201 | Fixed-effects model |
| Sex | ||||||
| Male | 10 | 1.03 (0.96, 1.10) | 0.408 | 49.2 | 0.038 | Fixed-effects model |
| Female | 10 | 1.12 (1.03, 1.22) | 0.007 | 24.7 | 0.216 | Fixed-effects model |
| Geographic area | ||||||
| USA | 13 | 0.99 (0.92, 1.06) | 0.782 | 29.2 | 0.168 | Fixed-effects model |
| Europe | 4 | 0.97 (0.86, 1.10) | 0.637 | 20.7 | 0.286 | Fixed-effects model |
| Canada | 3 | 1.17 (0.93, 1.48) | 0.178 | 6.4 | 0.344 | Fixed-effects model |
| Australia | 2 | 1.26 (0.97, 1.64) | 0.079 | 0.0 | 0.785 | Fixed-effects model |
| People’s Republic of China | 2 | 1.11 (1.03, 1.20) | 0.008 | 0.0 | 0.920 | Fixed-effects model |
| Age at start smoking (years) | ||||||
| Younger (≤20) | 3 | 1.15 (0.95, 1.39) | 0.145 | 42.1 | 0.178 | Fixed-effects model |
| Older (>20) | 3 | 1.25 (1.02, 1.52) | 0.029 | 0.0 | 0.553 | Fixed-effects model |
| Duration (years) | ||||||
| Short-term (≤20) | 5 | 0.97 (0.76, 1.24) | 0.799 | 50.3 | 0.090 | Random-effects model |
| Long-term (>20) | 6 | 1.06 (0.90, 1.26) | 0.473 | 58.1 | 0.036 | Random-effects model |
| Intensity (years) | ||||||
| Light (≤20) | 7 | 1.02 (0.96, 1.09) | 0.547 | 41.9 | 0.112 | Fixed-effects model |
| Heavy (>20) | 7 | 1.11(0.91, 1.35) | 0.309 | 65.4 | 0.008 | Random-effects model |
| Pack-years | ||||||
| Light (≤15) | 4 | 1.16 (0.96, 1.42) | 0.132 | 0.0 | 0.821 | Fixed-effects model |
| Heavy (>15) | 7 | 0.91 (0.80, 1.06) | 0.218 | 28.4 | 0.211 | Fixed-effects model |
| Year of study publication | ||||||
| Before 1990 | 7 | 0.91 (0.78, 1.07) | 0.261 | 18.1 | 0.292 | Fixed-effects model |
| 1990–2000 | 5 | 1.14 (1.00, 1.30) | 0.055 | 0.0 | 0.908 | Fixed-effects model |
| 2000–2010 | 5 | 1.09 (0.93, 1.26) | 0.284 | 50.7 | 0.088 | Random-effects model |
| 2010–now | 5 | 1.04 (0.97, 1.10) | 0.293 | 49.2 | 0.096 | Fixed-effects model |
Abbreviations: CI, confidence interval; RR, relative risk.