Table 1.
Quality assessment of included case control studies using the Newcastle-Ottawa scale
| Author | Yr |
Selection |
Comparability |
Exposure |
Score | ||||||
| Case definition | Case representativeness | Control selection | Control definition | Important confounders | Every confounders | Ascertainment | Consistency | Non-response rate | |||
| Low et al[7] | 2011 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 7 |
| Takhshid et al[2] | 2015 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| Daher et al[8] | 2011 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Han et al[4] | 2012 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 7 |
| Gao et al[10] | 2016 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Luan et al[13] | 2015 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Li et al[12] | 2017 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Li et al[11] | 2013 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| Zhang et al[14] | 2014 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Beltcheva et al[1] | 2014 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 7 |
| Pawlik et al[3] | 2017 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| Chen et al[15] | 2011 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| Wang et al[16] | 2016 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
The quality evaluation content mainly includes three aspects: case selection, baseline comparability, and exposure factors with nine evaluation items. If the evaluation item is met, 1 point is obtained, otherwise 0, and the score ranges from 0 to 9.