Table 2.
Results of the subgroup analysis.
| Subgroup | All | US | Non-US | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Studies | OR (95% CI) | I2, p-value | Studies | OR (95% CI) | I2, p-value | Studies | OR (95% CI) | I2, p-value | |
| Age at diagnosis | NA* | NA* | NA* | ||||||
| Premenopausal | 2 | 1.71 (1.36; 2.15) | 0%, 0.49 | NA | NA | NA | NA | NA | NA |
| Postmenopausal | 2 | 1.30 (1.05; 1.60) | 86%, < 0.01 | NA | NA | NA | NA | NA | NA |
| Study design | 0.29* | 0.51* | 0.34* | ||||||
| Case control | 7 | 1.23 (1.10; 1.38) | 36%, 0.16 | 4 | 1.20 (1.03; 1.39) | 0%, 0.51 | 3 | 1.28 (1.06; 1.55) | 70%, 0.03 |
| Cohort | 1 | 2.02 (0.81; 5.03) | NA | 0 | NA | NA | 1 | 2.02 (0.81; 5.03) | NA |
| Year | 0.91* | 0.65* | 0.34* | ||||||
| > 2000 | 3 | 1.23 (1.06; 1.44) | 0%, 0.53 | 2 | 1.22 (1.04; 1.42) | 0%, 0.73 | 1 | 2.02 (0.81; 5.03) | NA |
| < 2000 | 5 | 1.25 (1.05; 1.48) | 56%, 0.06 | 2 | 1.09 (0.71; 1.69) | 49%, 0.16 | 3 | 1.28 (1.06; 1.55) | 70%, 0.03 |
| Continent | 0.26* | NA* | 0.33* | ||||||
| America | 5 | 1.20 (1.06; 1.36) | 0%, 0.68 | 4 | 1.20 (1.03; 1.39) | 0%, 0.51 | 1 | 1.20 (0.97; 1.49) | NA |
| Europe | 2 | 1.55 (1.06; 2.27) | 82%, 0.02 | NA | NA | NA | 2 | 1.55 (1.06; 2.27) | 82%, 0.02 |
| Asia | 1 | 2.02 (0.81; 5.03) | NA | NA | NA | NA | 1 | 2.02 (0.81; 5.03) | NA |
| Country | 0.49* | NA* | NA* | ||||||
| US | 4 | 1.20 (1.03; 1.39) | 0%, 0.51 | 4 | 1.20 (1.03; 1.39) | 0%, 0.51 | NA | NA | NA |
| Non-US | 4 | 1.30 (1.09; 1.57) | 61%, 0.05 | NA | NA | NA | 4 | 1.30 (1.09; 1.57) | 61%, 0.05 |
| Population | 0.99* | 0.62* | 0.31* | ||||||
| > 1000 | 3 | 1.24 (1.07; 1.43) | 0%, 0.56 | 1 | 1.24 (1.02; 1.52) | NA | 2 | 1.55 (1.06; 2.27) | 82%, 0.02 |
| < 1000 | 5 | 1.24 (1.03; 1.50) | 57%, 0.05 | 3 | 1.15 (0.92; 1.44) | 2%, 0.36 | 2 | 1.24 (1.00; 1.53) | 14%, 0.28 |
| NOS risk of bias | NA* | NA* | NA* | ||||||
| High quality | 3 | 1.23 (1.06; 1.44) | 0%, 0.53 | 2 | 1.22 (1.04; 1.42) | 0%, 0.73 | 1 | 2.02 (0.81; 5.03) | NA |
*, p-value of subgroup differences; NA, Not Applicable.