Table 2. Methodological quality of case-control studies in our meta-analyses, based on the Newcastle–Ottawa Scale.
| Study | Selection (score) | Comparability (score) | Exposure (score) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Adequate definition of patient cases | Representativeness of patients/cases | Selection of controls | Definition of controls | Control for important factor or additional factor | Ascertainment of exposure (blinding) | Same method of ascertainment for participants | Non-response ratea | Total scoreb | |
| Migita et al.12 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 5 |
| Kim et al.13 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 5 |
| Chen et al.14 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Teixeira et al.15 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 6 |
| Karra et al.16 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 5 |
| Bao et al.17 | 1 | 1 | 1 | 1 | 2 | 0 | 1 | 1 | 8 |
| Zhang et al.18 | 1 | 1 | 1 | 1 | 2 | 0 | 1 | 1 | 8 |
| Lau et al.19 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 6 |
aOne point was awarded when there was no significant difference in the response rate between both groups based on the chi-squared test (P > 0.05).
bCalculated by adding up the points awarded for each item.