Table 1.
Quality of the included studies based on the Newcastle–Ottawa scale
| Studies | Selection
|
Comparability | Outcome
|
Total score | |||||
|---|---|---|---|---|---|---|---|---|---|
| Representativeness of the exposed cohort | Selection of the nonexposed cohort | Assessment of exposure | Outcome not present at start of study | Assessment of outcome | Follow-up long enough for outcomes | Adequacy of follow-up | |||
| Zhou et al18 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 6 |
| Yu et al26 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 6 |
| Zhang19 | 1 | 1 | 1 | 0 | 1 | 0 | 1 | 0 | 5 |
| Ahn et al30 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 |
| Zhang et al27 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 5 |
| Zhang et al28 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 0 | 5 |
| Pan et al29 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 0 | 5 |
Notes:
*
A study can be awarded a maximum of one point for each numbered item within the “Selection” and “Outcome” categories, and a maximum of two points can be given for “Comparability”.