Table 1.

Hierarchy of evidence

Level	ES document (used for effect size estimation)	Included studies
1	A review of reviews of RCTs	Overview; umbrella review; meta-review; (systematic) review of (systematic) reviews
2	A systematic review of RCTs from Cochrane collaboration	Systematic review, meta-analysis and their combination
3	Other systematic review of RCTs	Systematic review, meta-analysis and their combination
4	RCTs in which case they were considered equally relevant ES documents from which we calculated the combined effect size	RCTs
5	Non-randomised controlled studies in cases were true randomisation was not feasible or ethical	Non-randomised controlled studies