References	Risk of bias (RoB) domains a								Tier b
	Exposure KEY	Outcome KEY	Randomization KEY	Allocation concealment	Blinding	Attrition	Reporting	Other threats to internal validity
Durga et al. ( 2007 )	+	++	++	++	++	++	+	+	1

^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).