Table 3 Quality assessment of included articles (n = 25)
Reference | Sampling (4 points) | Confounders controlled (2 points) | Exposure (3 points) | Total rating (9 points) |
|---|---|---|---|---|
[37] | – − − − | – − | + + − | 2 |
[60] | – − − − | + − | + + − | 3 |
+ − − − | – − | + + + | 4 | |
[41] | – − − − | + − | + + + | 4 |
+ − − − | + − | + + + | 5 | |
[55] | + + − − | – − | + + + | 5 |
[45] | + − − + | –  − | + + + | 5 |
+ − − − | + + | + + + | 6 | |
[42] | + + − − | + − | + + + | 6 |
+ + − − | + + | + + + | 7 | |
+ − − + | + + | + + + | 7 | |
[50] | + + + − | + + | + + + | 8 |