Table 2. Summary RR and 95%CI of the association between dietary vitamin A intake and ovarian cancer risk.
| Subgroups | Number of studies | Number of cases | RR(95% CI) | P for trend | Heterogeneity test | |
|---|---|---|---|---|---|---|
| I2 (%) | P | |||||
| Overall | 15 | 4882 | 0.816(0.723–0.920) | 0.001 | 48.4 | 0.019 |
| Study design | ||||||
| Cohort | 5 | 1435 | 0.895(0.736–1.088) | 0.264 | 0.0 | 0.797 |
| Case–control | 10 | 3447 | 0.769(0.655–0.902) | 0.001 | 64.6 | 0.003 |
| PBCC | 5 | 1969 | 0.812(0.651–0.994) | 0.037 | 55.3 | 0.062 |
| HBCC | 5 | 1478 | 0.712(0.551–0.922) | 0.010 | 64.8 | 0.023 |
| Geographic locations | ||||||
| North America | 12 | 3984 | 0.825(0.720-0.946) | 0.006 | 38.4 | 0.088 |
| Europe | 2 | 644 | 0.890(0.771–1.028) | 0.114 | 0.0 | 0.630 |
| Asia | 1 | 254 | – | – | – | – |
Abbreviations: CI, confidence interval; HBCC, hospital-based case–control studies; PBCC, population-based case–control studies; RR, relative risk.