Table 2. Quality assessment of studies included in meta-analysis.
| Follow up duration | First author (year) | Representativeness of both cohorts | Quality of data records | Comparability of cohorts | Outcome assessment | Relevant follow-up period | Important confounders/prognostic factors Identified |
|---|---|---|---|---|---|---|---|
| Short-term (FU 12 mo < x < 24 mo) | Hou et al. (2014) (18) | Average | Excellent | Average | Excellent | Good | Poor |
| Li et al. (2014) (19) | Average | Good | Average | Good | Good | Good | |
| Tracey et al. (2014) (20) | Good | Good | Good | Average | Good | Poor | |
| Rožanković et al. (2014) (21) | Good | Good | Good | Good | Good | Poor | |
| Kang et al. (2013) (22) | Poor | Good | Good | Good | Good | Poor | |
| Zhang et al. (2012) (23) | Excellent | Good | Good | Good | Good | Good | |
| Auerbach et al. (2011) (24) | Good | Good | Good | Good | Good | Good | |
| Coric et al. (2011) (8) | Good | Average | Good | Average | Good | Poor | |
| Hisey et al. (2011) (25) | Excellent | Good | Good | Poor | Good | Poor | |
| Kelly et al. (2011) (26) | Excellent | Average | Good | Poor | Good | Good | |
| Park et al. (2011) (27) | Good | Good | Good | Good | Good | Average | |
| Anakwenze et al. (2009) (28) | Good | Average | Good | Average | Good | Average | |
| Cheng et al. (2009) (29) | Poor | Poor | Good | Good | Good | Poor | |
| Heller et al. (2009) (30) | Good | Good | Good | Average | Good | Good | |
| Kim et al. (2009) (31) | Good | Good | Good | Good | Good | Good | |
| Anderson et al. (2008) (32) | Good | Good | Average | Good | Good | Good | |
| Peng-Fei et al. (2008) (33) | Poor | Poor | Average | Poor | Good | Poor | |
| Sasso et al. (2008) (34) | Good | Average | Good | Average | Good | Average | |
| Mummaneni et al. (2007) (10) | Good | Average | Good | Poor | Good | Poor | |
| Nabhan et al. (2007) (35) | Poor | Poor | Poor | Good | Good | Poor | |
| Long-term (>24 mo) | Davis et al. (2015) (9) | Excellent | Good | Good | Poor | Good | Poor |
| Burkus et al. (2014) (36) | Average | Good | Good | Excellent | Excellent | Poor | |
| Coric et al. (2013) (37) | Poor | Good | Good | Poor | Excellent | Poor | |
| Zigler et al. (2012) (38) | Excellent | Good | Good | Poor | Excellent | Poor | |
| Sasso et al. (2011) (39) | Good | Good | Good | Excellent | Excellent | Good | |
| Burkus et al. (2010) (40) | Average | Good | Good | Poor | Excellent | Poor | |
| Delamarter et al. (2010) (41) | Excellent | Good | Good | Excellent | Excellent | Average | |
| Garrido et al. (2010) (42) | Poor | Good | Good | Poor | Excellent | Average |
FU, Follow up; mo, month.