| Confounding factor | Studies controlling for factor (Total = 09) | % |
| Age | 08 | 88.8 |
| Socioeconomic status | 03 | 33.3 |
| Education | 04 | 44.4 |
| Race/Ethnicity | 05 | 55.5 |
| Partnership status | 06 | 66.6 |
| Parity | 08 | 88.8 |
| Weight/Body mass index | 07 | 77.7 |
| Menopausal Status | 08 | 88.8 |
| Hormone replacement | 02 | 22.2 |