Table 1. Effect of body mass index on incidence of breast cancer by quality of the studies, menopausal period, and study design.
| High Quality | Moderate Quality | Low Quality | ||||
| Period | Effect Size | Q-test | Effect Size | Q-test | Effect Size | Q-test |
| Study design | (95% CI) | P value | (95% CI) | P value | (95% CI) | P value |
| Premenopausal | ||||||
| Case-control (OR) | 0.93 (0.84, 1.02) | 0.001 | 0.98 (0.79, 1.21) | 0.020 | No data | - |
| Cohort (RRi) | No data | - | 0.97 (0.82, 1.16) | 0.020 | No data | - |
| Cohort (RRa) | 1.02 (0.92, 1.13) | 0.360 | 0.98 (0.91, 1.05) | 0.010 | No data | - |
| Postmenopausal | ||||||
| Case-control (OR) | 1.18 (1.08, 1.29) | 0.001 | 1.08 (0.96, 1.22) | 0.001 | No data | - |
| Cohort (RRi) | 1.01 (0.93, 1.10) | 0.010 | 1.11 (1.06, 1.16) | 0.020 | 1.22 (1.13, 1.32) | 0.040 |
| Cohort (RRa) | 0.99 (0.90, 1.08) | 0.001 | 0.96 (0.60, 1.54) | 0.001 | No data | - |