3. Risk of bias assessment.

Trial	Concealment of allocation	Follow‐up of professionals	Follow‐up of patients or episodes of care	Blinded assessment of primary outcome(s)	Baseline measurement	Reliable primary outcome measure(s)	Protection against contamination	Overall risk of bias
Abelson 2003	Not clear	Not relevant	Not done	Not clear	Done	Done	Done	High
Chumbley 2002	Done	Not relevant	Done	Not clear	Not clear	Done	Done	Moderate
Clark 1999	Not clear	Not relevant	Done	Not clear	Done	Done	Done	Moderate
Aabakken 1997	Done	Not relevant	Done	Not clear	Not clear	Done	Done	Moderate
Polowczyk 1993	Not clear	Not relevant	Done	Not clear	Done	Done	Done	Moderate
Guarino 2006	Not clear	Not relevant	Not done	Not clear	Done	Not clear	Done	High