Table 3.
The risk of bias in all the included studies (top-down) according to Cochrane Collaboration’s biases tool (from left to right). The plus sign indicating low risk of bias whereas the minus sign indicates high risk of bias. The question mark indicates an unknown risk of bias
| Random sequence generation (selection bias) | Allocation concealment (selection bias) | Blinding of participants (performance bias) | Blinding of practitioners (performance bias) | Blinding of outcome assessment (detection bias) | Incomplete outcome data (attrition bias) | Selective reporting (reporting bias) | Other bias | |
|---|---|---|---|---|---|---|---|---|
| Alimi 2012 [26] | + | + | + | – | + | + | – | + |
| Blom 1992 [27] | + | – | + | – | + | – | + | – |
| Blom 1996 [28] | + | – | + | – | + | – | + | – |
| Braga 2011 [29] | – | – | – | – | – | + | + | – |
| Cho 2008 [33] | + | + | + | – | +/? | + | + | – |
| List 1998 [30] | + | – | – | – | −/+ | – | – | – |
| Meng 2012 [31] | + | + | – | – | −/? | – | + | + |
| Meng 2012 [32] | + | + | + | – | +/? | – | + | + |
| Pfister 2010 [34] | + | + | – | – | – | + | + | – |
| Simcock 2013 [35] | + | + | – | – | – | – | + | + |
+ = low risk of bias
- = high risk of bias
? = unknown risk of bias