Table 2. Details of quality evaluation by the Newcastle–Ottawa Scale.
| Studies | Representativeness of the exposed cohort | Selection of the non-exposed cohort | Ascertainment of exposure | Outcome of interest not present at baseline | Adjustment of age and gender | Adjustment of other confounding factors | Assessment of outcome | Follow-up long enough | Adequacy of follow-up of cohorts | Total |
|---|---|---|---|---|---|---|---|---|---|---|
| Rauuncolo, 2002 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 6 |
| Wei, 2010 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 5 |
| Sooman, 2014 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 6 |
| Guadagno, 2016 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 6 |
| Pinel, 2017 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Tsidulko, 2017 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Nishikawa, 2018 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 5 |
| Bien-Möller, 2018 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 7 |
| Alameda, 2019 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Hou, 2019 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 7 |
| Dong, 2019a | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 7 |
| Dong, 2019b | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 7 |
The study Dong 2019 included stratified datasets in patients with WHO grade II–III glioma and glioblastoma, which were included in the meta-analysis separately.