4. Distribution of risk of bias in included studies.
| Bias/study design | Randomised controlled trial | Controlled before‐after study | Interrupted time series |
| Allocation (selection bias) |
Unclear: Fairbrother 1999, Fairbrother 2001, Christensen 2000, Davidson 1992, Kouides 1998, Lurie 1992 High: Houle 2016, Twardella 2007 Low: Bilardi 2010, Hickson 1987, Petersen 2013, Clarkson 2008 |
High: Gosden 2003, Gray 2015, Chung 2010, Flierman 1992, Jensen 2014, Lee 2010, Li 2013, Singh 2015, Greene 2013, Yesalis 1980, Yesalis 1984, Krasnik 1990, Gleeson 2017 | High: Young 2012, Young 2007 |
| Blinding (performance bias and detection bias) |
Unclear: Fairbrother 1999, Fairbrother 2001, Hickson 1987, Kouides 1998 High: Lurie 1992 Low: Bilardi 2010, Christensen 2000, Clarkson 2008, Davidson 1992, Houle 2016, Petersen 2013, Twardella 2007 |
Unclear: Li 2013, Singh 2015 High: Gosden 2003 Low: Gleeson 2017, Gray 2015, Greene 2013, Chung 2010, Flierman 1992, Jensen 2014, Lee 2010, Yesalis 1980, Yesalis 1984, Krasnik 1990 |
Low: Young 2007, Young 2012 |
| Incomplete outcome data (attrition bias) |
Unclear: Bilardi 2010, Clarkson 2008 High: Twardella 2007 Low: Christensen 2000, Fairbrother 1999, Fairbrother 2001, Hickson 1987, Houle 2016, Kouides 1998, Lurie 1992, Petersen 2013, Davidson 1992 |
Unclear: Chung 2010, Gosden 2003, Lee 2010 Flierman 1992, Jensen 2014, Greene 2013, Yesalis 1980, Yesalis 1984, Gleeson 2017 High: Gray 2015 Low: Li 2013, Singh 2015, Krasnik 1990 |
Low: Young 2007, Young 2012 |
| Selective reporting (reporting bias) |
Unclear: Clarkson 2008 Low: Bilardi 2010, Christensen 2000, Davidson 1992, Fairbrother 1999, Fairbrother 2001, Hickson 1987, Houle 2016, Kouides 1998, Lurie 1992, Petersen 2013, Twardella 2007 |
Unclear: Chung 2010, Lee 2010, Greene 2013 Low: Gosden 2003, Gray 2015, Flierman 1992, Jensen 2014, Li 2013, Singh 2015, Yesalis 1980, Yesalis 1984, Krasnik 1990, Gleeson 2017 |
Low: Young 2007, Young 2012 |