Table 2.
Quality assessment of the included studies.
| First author, year | Selection1 | Comparability2 | Outcome3 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Representativeness of exposed cohort ★ | Selection of nonexposed cohort ★ | Ascertainment of exposure ★ | No primary outcome was present at the start of study ★ | Comparable on confounder ★★ | Outcome assessment ★ | Adequate follow-up ★ | Loss to follow-up ★ | Total score | |
| Adams et al., 2009 | ★ | ★ | ★ | ★★ | ★ | ★ | 7 | ||
| Betge et al., 2016 | ★ | ★ | ★ | ★ | ★ | ★ | ★ | ★ | 8 |
| Elzagheid et al., 2013 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
| Imai et al., 2013 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
| Kang et al., 2011 | ★ | ★ | ★ | ★ | ★ | ★ | ★ | 7 | |
| Khanh et al., 2013 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
| Lu et al., 2014 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
| Perez et al., 2008 | ★ | ★ | ★ | ★ | ★ | ★ | ★ | 7 | |
| Wang et al., 2017 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
| Yu et al., 2007 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
| Zwenger et al., 2014 | ★ | ★ | ★ | ★★ | ★ | ★ | ★ | 8 | |
1“Selection” part includes representativeness of cases, selection of controls, exposure ascertainment, and no death when investigation begins. 2“Comparability” part includes comparable on confounders. 3“Outcome” part includes outcome assessment, adequate follow-up, and loss to follow-up rate. ★ represents score of 1. ★★ represents score of 2.