Table 1.

Level of evidence

Evidence level	Study design	Internal validity (risk of bias assessment)
High	RCT or SR/meta-analysis or non-randomized diagnostic study (cohort or cross-sectional)	No concern
Moderate	RCT or non-randomized diagnostic study (cohort or cross-sectional)	Minor concerns with limitations in the major area of each quality appraisal tool
	Prospective cohort study
Low	Retrospective cohort study or non-randomized diagnostic study (cohort or cross-sectional) or case-control study	Severe concerns with limitations in the major area of each quality appraisal tool

RCT, randomized controlled trial; SR, systematic review.