Table 2. Summary of Within Study Bias for Each Studya,b.
| Author | Types of Bias (17) | |||
|---|---|---|---|---|
| Year | Selection | Measurement | Confounding | |
| Butler ( 19 ) | 1997 | ++ | +++ | +++ |
| Butler ( 20 ) | 1999 | ++ | +++ | +++ |
| Roberts ( 21 ) | 2000 | +++ | +++ | +++ |
| Gilles ( 22 ) | 2008 | ++ | ++ | ++ |
| Van Der Poorten ( 23 ) | 2008 | ++ | ++ | ++ |
| Templeton ( 24 ) | 2010 | ++ | ++ | ++ |
| Ward ( 25 ) | 2011 | +++ | ++ | +++ |
| Davies ( 26 ) | 2012 | +++ | ++ | ++ |
| Paquette ( 27 ) | 2013 | +++ | +++ | +++ |
| Su ( 33 ) | 2013 | ++ | ++ | +++ |
| Foy ( 28 ) | 2014 | +++ | +++ | +++ |
| Luciani ( 29 ) | 2014 | ++ | ++ | +++ |
| Parker ( 30 ) | 2014 | ++ | ++ | ++ |
| Harrod ( 31 ) | 2014 | ++ | ++ | ++ |
| Saulo ( 32 ) | 2014 | ++ | ++ | +++ |
aJudgment: Risk of bias, + = Low, ++ = Medium, +++ = High.
bA more detailed description of bias for each study is included in Appendix 1.