Table 2.
Methodological quality assessment according to Newcastle-Ottawa Scale (NOS)
| Study | Selection | Comparability | Exposure/outcome | Total score | |||||
|---|---|---|---|---|---|---|---|---|---|
| Adequate definition of case/exposed cohort | Representativeness of the cases/ exposed cohort | Selection of Controls | Definition of Controls | Comparability of cases and controls (worth 2 points) | Ascertainment of exposure/outcome | Same method of ascertainment for cases and controls/long enough for outcomes to occur | Non-Response Rate | ||
| Alehagen 2015 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 7 |
| Bleys 2007 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 1 | 9 |
| Gao 2014 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 1 | 9 |
| Laclaustra 2009 | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 1 | 9 |
| Stranges 2011 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 7 |