Table 1.

Evidence level and quality of study design.

Grade	Design
AA	Systematic review or meta-analysis of randomized trials
A	Systematic review or meta-analysis of non-randomized controlled
	Randomized trial or cluster randomized trial
B	Systematic review or meta-analysis of controlled studies without a pretest or uncontrolled study with a pretest
	Non-randomized trial
	Controlled before-after study
	Retrospective or prospective cohort study
	Interrupted time series
C	Systematic review or meta-analysis of cross-sectional studies
	Non-controlled before-after study
D	Cross-sectional study
E	Case studies, case reports, traditional literature reviews, theoretical papers