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| Group | Pooled Effect Estimate (95 % CI) | I2 % | Number of Observations |
| All studies | 1.44 (1.22, 1.70) | 70.5 | 35 |
| Case-control studies | 1.58 (1.28, 1.95) | 68.9 | 24 |
| Cohort studies | 1.19 (0.87, 1.62) | 75.6 | 11 |
| Asia | 1.86 (1.07, 3.22) | 0 | 2 |
| Canada | 1.25 (0.97, 1.61) | 60.8 | 9 |
| Europe | 1.43 (1.09, 1.89) | 39.3 | 7 |
| USA | 1.51 (1.16, 1.95) | 65.1 | 17 |
