Table 2. Quality assessment based on the Newcastle-Ottawa Scale of studies included in this meta-analysis a .
| First author | Year | Adequate definition of case | Representativeness of cases | Selection of control | Definition of control | Control for important factor or additional factor b | Exposure assessment | Same method of ascertainment for cases and controls | Nonresponse rate | Total quality scores |
|---|---|---|---|---|---|---|---|---|---|---|
| Ebisch | 2003 | ★ | ★ | ★ | ★ | ★★ | ★ | 7 | ||
| Stuppia | 2003 | ★ | ★ | ★★ | ★ | 5 | ||||
| Park | 2005 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Singh | 2005 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Lee | 2006 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Paracchini | 2006 | ★ | ★ | ★ | ★ | ★ | ★ | 6 | ||
| A | 2007 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Sun | 2007 | ★ | ★ | ★ | ★ | ★ | 5 | |||
| Ravel | 2009 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Yang | 2010 | ★ | ★ | ★ | ★ | ★ | 5 | |||
| Gava (37) | 2011 | ★ | ★ | ★ | ★ | ★★ | ★ | 7 | ||
| Gava (49) | 2011 | ★ | ★ | ★ | ★ | ★★ | ★ | 7 | ||
| Safarinejad | 2011 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Murphy | 2011 | ★ | ★ | ★ | ★ | ★★ | ★ | 7 | ||
| Qiu | 2011 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Gupta | 2011 | ★ | ★ | ★ | ★ | ★ | 5 | |||
| Eloualid | 2012 | ★ | ★ | ★★ | ★ | 5 | ||||
| Chellat | 2012 | ★ | ★ | ★ | ★ | ★ | 5 | |||
| Vani | 2012 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Liu | 2012 | ★ | ★ | ★ | ★ | ★★ | ★ | 7 | ||
| Camprubí | 2013 | ★ | ★ | ★ | ★ | ★ | ★ | 6 | ||
| Pei | 2013 | ★ | ★ | ★ | ★ | ★★ | ★ | 7 | ||
| Weiner | 2013 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Naqvi | 2014 | ★ | ★ | ★ | ★ | ★ | 5 | |||
| Mfady | 2014 | ★ | ★ | ★ | ★★ | ★ | 6 | |||
| Li | 2014 | ★ | ★ | ★ | ★★ | ★ | 6 |
aA study can be awarded a maximum of one star for each numbered item except for the item Control for important factor or additional factor.
bA maximum of two stars can be awarded for Control for important factor or additional factor.