Table 4. Newcastle-Ottawa Scale for Risk of Bias.
| Study ID | Catena et al, 2008 [1] | Nishimura et al, 2007 [3] | Karakousis et al, 2011 [10] | Matthews et al, 2002 [11] | Pitisinis et al, 2007 [12] | Silberhumer et al, 2009 [13] | Wu et al, 2012 [14] |
|---|---|---|---|---|---|---|---|
| Study design | Retrospective cohort | Retrospective cohort | Case-control study | Retrospective cohort | Retrospective cohort | Retrospective cohort | Retrospective cohort |
| Selection | **** | **** | **** | **** | **** | **** | **** |
| Comparability | * | ||||||
| Outcome/exposure | *** | *** | *** | *** | *** | *** | *** |