References	Risk of bias domains (a)							Tier (b)
	Exposure KEY	Outcome KEY	Randomisation KEY	Allocation concealment	Blinding	Attrition	Other threats to internal validity
Berger et al. ( 1992 )	NR	+	−−	−−	−−	−	−	2

^(a)Expert judgement was translated into a rating scale for each question to be answered as follows: (++): definitely low RoB; (+): probably low RoB; (NR): not reported; (−): probably high RoB; (− −): definitively high RoB.

^(b)The individual rating for each question was combined by an algorithm and translated to an overall tier of reliability for each individual study (RoB tier 1: low RoB; RoB tier 2: moderate RoB; RoB tier 3: high RoB).