Table 2.
NOS scores of the case-control studies included.
| Case-control study | Is the case definition adequate? | Representativeness of the cases | Selection of Controls | Definition of Controls | Control for important factor* | Control for additional factor* | Ascertainment of exposure* | Same method of ascertainment for cases and controls | Non-Response rate | Total quality scores |
|---|---|---|---|---|---|---|---|---|---|---|
| Chen et al. (2021) | ★ | ★ | ★ | ★ | ★ | ★ | ★ | ★ | / | 8 |
| Xu et al. (2020) | ★ | ★ | ★ | ★ | ★ | / | / | ★ | / | 6 |
| Koga et al. (2020) | ★ | ★ | ★ | ★ | ★ | ★ | ★ | ★ | / | 7 |
| Zheng et al. (2018) | ★ | ★ | ★ | ★ | ★ | ★ | / | ★ | / | 8 |
| Krishnasamy et al. (2017) | ★ | ★ | ★ | ★ | ★ | ★ | ★ | ★ | / | 8 |
| Di Lullo et al. (2015) | ★ | ★ | / | / | ★ | ★ | ★ | / | / | 5 |
| Cai et al. (2015) | ★ | ★ | ★ | ★ | ★ | ★ | ★ | ★ | / | 8 |
| Morita et al. (2015) | ★ | / | ★ | ★ | ★ | ★ | ★ | ★ | / | 7 |
| Buiten et al. (2014) | ★ | ★ | ★ | ★ | ★ | ★ | ★ | ★ | / | 8 |
| Kitagawa et al. (2013) | ★ | ★ | / | / | ★ | ★ | ★ | / | / | 5 |
*
2 stars could be awarded for this item. Studies that controlled for age or renal function or indicators of calcium and phosphorus metabolism was awarded one star, respectively.
NOS, Newcastle–Ottawa Scale.