Table 1 Risk of bias
| Â | Selection bias | Confounding bias | Outcome measurement bias |
|---|---|---|---|
Bruno (2007) [34] | Low | Moderate | Low |
Giron-Gonzalez (2007) [29] | Unclear | Moderate | Low |
Limketkai (2012) [23] | Low | Low | Low |
Macias (2006) [25] | Low | Moderate | Low |
Macias (2009) [24] | Low | Low | Unclear |
Mariné-Barjoan (2004) [35] | Low | High | Low |
Mehta (2005) [30] | Unclear | High | High |
Merchante (2006) [31] | Unclear | High | Low |
Pineda (2009) [32] | Low | Moderate | Low |
Qurishi (2003) [26] | Unclear | Low | Low |
Ragni (2009) [27] | Low | Low | Unclear |
Reiberger (2010) [36] | Low | High | Low |
Sanmartin (2014) [33] | Low | High | High |
Schiavini (2006) [28] | Unclear | High | Low |
Total risk of bias | 9 low | 4 low | 10 low |
0 high | 6 high | 2 high | |
5 unclear | 4 moderate | 2 unclear |