Table 2.
Assessing risk of bias
| First author year | Sequence generation | Allocation concealment | Blinding | Incomplete outcome data addressed | Selective outcome reporting | Free of other bias | Summary risk of bias |
|---|---|---|---|---|---|---|---|
| Nelson 1998 [37] | Unclear | Unclear | Yes | Yes | Yes | Yes | Unclear |
| Nelson 2000 [38] | Unclear | Unclear | Yes | Yes | Yes | Yes | Unclear |
| Tanaka 2001 [39] | Unclear | Unclear | Unclear | Yes | Yes | Yes | Unclear |
| Wund 2001 [40] | Unclear | Unclear | Yes | Yes | Yes | Yes | Unclear |
| Presneill 2002 [41] | Yes | Yes | Yes | Yes | Yes | Yes | Low |
| Root 2003 [42] | Yes | Unclear | Yes | Unclear | Yes | Yes | Unclear |
| Hartma 2005 [43] | Yes | Yes | Yes | Yes | Yes | Yes | Low |
| Rosen 2005 [44] | Unclear | Yes | No | Yes | Yes | Yes | High |
| Orozco 2006 [45] | Unclear | Unclear | Yes | Yes | Yes | Yes | Unclear |
| Cheng 2007 [46] | Yes | Yes | Yes | Yes | Yes | Yes | Low |
| Stephens 2008 [47] | Yes | Yes | Yes | Yes | Yes | Yes | Low |
| Meisel 2009 [48] | Yes | Yes | Yes | Yes | Yes | Yes | Low |