Table 6.
Application of the Newcastle–Ottawa scale for case-control studies in order to evaluate the risk of bias of the five studies selected for the present systematic review.
| Selection | Comparability | Exposure | Score | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Study | Definition of cases | Representativeness of cases | Selection of controls | Definition of controls | Comparability of cases and controls on the basis of the design or analysis | Ascertainment of exposure | Same method of ascertainment for cases and controls | Nonresponse rate | |
| Kumar et al. [12] | 3 | 3 | 3 | 3 | 2 | 3 | 3 | 1 | 21 |
| Raju et al. [16] | 3 | 3 | 3 | 3 | 2 | 3 | 3 | 1 | 21 |
| Venkatasubramanian et al. [17] | 3 | 3 | 3 | 3 | 2 | 3 | 3 | 1 | 21 |
| Hurtt and Rossman [18] | 3 | 3 | 3 | 3 | 1 | 2 | 3 | 1 | 19 |
| Morrison and Conrod [19] | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 1 | 15 (unsuitable) |