Table 1. Risk of bias assessment by the 7 key categories of the Cochrane risk of bias tool.
| First author, year of publication | Selection bias | Attrition bias | Reporting bias | Performance bias | Incomplete analysis according to group allocation | Detection bias | Other bias |
|---|---|---|---|---|---|---|---|
| Abbott, 2009 | high risk | high risk | Unclear | high risk | low risk | low risk | low |
| Andersson, 2002 | Unclear | high risk | Unclear | low risk | Unclear | low risk | high |
| Andersson, 2003 | Unclear | high risk | Unclear | low risk | Unclear | low risk | high |
| Boer, de, 2014 | high risk | high risk | Unclear | Unclear | high risk | low risk | high |
| Brattberg, 2006 | low risk | high risk | Unclear | Unclear | Unclear | low risk | low |
| Buhrman, 2004 | high risk | high risk | Unclear | low risk | Unclear | low risk | low |
| Buhrman, 2011 | low risk | Unclear | Unclear | low risk | low risk | low risk | low |
| Buhrman, 2013a | high risk | high risk | Unclear | Unclear | low risk | low risk | low |
| Buhrman, 2013b | Unclear | high risk | Unclear | Unclear | low risk | low risk | low |
| Buhrman, 2015 | high risk | Unclear | high risk | low risk | low risk | low | |
| Camerini, 2012 | Unclear | high risk | Unclear | high risk | Unclear | low risk | low |
| Carpenter, 2012 | Unclear | high risk | Unclear | low risk | Unclear | low risk | low |
| Chiauzzi, 2010 | high risk | high risk | Unclear | Unclear | low risk | low risk | low |
| Davis, 2013 | low risk | Unclear | Unclear | high risk | low risk | low risk | low |
| Dear, 2013 | Unclear | low risk | low risk | low risk | low risk | low risk | low |
| Dear, 2015 | low risk | Unclear | low risk | low risk | low risk | low risk | low |
| Devenini, 2005 | Unclear | high risk | Unclear | Unclear | Unclear | Unclear | low |
| Dowd, 2015 | Unclear | high risk | Unclear | high risk | low risk | low risk | low |
| Everitt, 2013 | high risk | Unclear | low risk | high risk | low risk | low risk | low |
| Hesser, 2012 | low risk | low risk | Unclear | low risk | low risk | low risk | low |
| Hunt, 2009 | Unclear | high risk | Unclear | high risk | high risk | low risk | high |
| Hunt, 2015 | Unclear | high risk | Unclear | Unclear | high risk | low risk | high |
| Janse, 2016 | Unclear | low risk | low risk | high risk | low risk | high risk | low |
| Jasper, 2014 | Unclear | low risk | low risk | low risk | low risk | low risk | low |
| Kaldo, 2008 | Unclear | low risk | Unclear | low risk | low risk | low risk | high |
| Krein, 2013 | low risk | low risk | Unclear | low risk | low risk | low | |
| Kristjánsdóttir, 2013 | low risk | high risk | Unclear | low risk | low risk | low risk | low |
| Lee, 2014 | Unclear | high risk | Unclear | Unclear | Unclear | low risk | low |
| Ljotsson, 2010 | Unclear | low risk | Unclear | low risk | low risk | low risk | low |
| Ljotsson, 2011a | low risk | low risk | Unclear | Unclear | low risk | low risk | low |
| Ljotsson, 2011b | low risk | high risk | Unclear | Unclear | low risk | low risk | low |
| Lorig, 2008 | Unclear | high risk | low risk | Unclear | low risk | low risk | low |
| Menga, 2014 | Unclear | high risk | Unclear | Unclear | Unclear | low risk | high |
| Moessner, 2014 | Unclear | high risk | Unclear | Unclear | low risk | low risk | low |
| Mourad, 2016 | high risk | low risk | low risk | low risk | low risk | low risk | high |
| Naylor, 2008 | low risk | low risk | Unclear | low risk | low risk | low risk | low |
| Oerlemans, 2011 | high risk | Unclear | high risk | low risk | Unclear | low risk | low |
| Riva, 2014 | low risk | low risk | Unclear | Unclear | low risk | low risk | low |
| Ruehlman, 2012 | Unclear | high risk | Unclear | Unclear | low risk | low risk | low |
| Schulz, 2007 | high risk | low risk | high risk | high risk | low risk | low risk | high |
| Strom, 2000 | Unclear | high risk | Unclear | high risk | Unclear | low risk | high |
| Trompetter, 2015 | Unclear | high risk | low risk | high risk | low risk | low risk | low |
| Vallejo, 2015 | Unclear | Unclear | Unclear | low risk | low risk | low risk | high |
| Weise, 2016 | Unclear | low risk | low risk | low risk | low risk | low risk | low |
| Williams, 2010 | Unclear | Unclear | Unclear | low risk | low risk | low risk | low |
| Wilson, 2015 | Unclear | high risk | Unclear | high risk | high risk | low risk | low |
The 13 risk of bias criteria of the Cochrane Collaboration Back Review Group were combined into these 7 major categories of the general Cochrane risk of bias tool.