Table 1.

Level of Evidence and Strength of Recommendation

	Explanation
Class
High	At least one RCT or SR/meta-analysis with no concern of study quality
Moderate	At least one RCT or SR/meta-analysis with minor concern of study quality or at least one cohort/case-control/diagnostic test design study with no concern of study quality
Low	At least one cohort/case-control/diagnostic test study with minor concern of study quality or at least one single arm before-after study, cross-sectional study with no concern of study quality
Very low	At least one cohort/case-control/diagnostic test design study with serious concern of study quality or at least one single arm before-after study, cross-sectional study with minor/severe concern of study quality
Grade classification
Strong for	The benefit of intervention is greater than harm with high or moderate level of evidence, which can be strongly recommended in most clinical practice.
Weak for	The benefit and harm of intervention may vary depending on the clinical situation or patient/social value. It is recommended conditionally according to the clinical situation.
Against	The benefit and harm of intervention may vary depending on the clinical situation or patient/social value. Intervention may not be recommended in clinical practice.
No recommendation	It is not possible to determine the recommendation direction owing to a lack of evidence or discrepancy of result. Thus further evidence is needed.

RCT, randomized controlled trial; SR, systematic review.