Table 1. Grading systems in Consensus Group recommendations.

Level	Type of evidence	Grades of recommendation
1a	Systematic review with homogeneity of randomized controlled trials	A (Grades of recommendation)
1b	Individual randomized controlled trials with a narrow confidence interval
1c	All or non-related outcome
2a	Systematic review with homogeneity of cohort studies	B (Grades of recommendation)
2b	Individual cohort studies (including low-quality randomized controlled trials)
2c	“Outcomes” research ecological studies
3a	Systematic review with homogeneity of case-control studies
3b	Individual case-control study
4	Case-series (and poor-quality cohort and case-controlled studies)	C (Level 4 studies or extrapolation from level 2 or 3 studies)
5	Expert opinion without explicit critical appraisal, or based on physiological/bench research	D (Level 5 studies or troublingly inconsistent or inconclusive studies of any level)

Levels of evidence are adapted from the Oxford Center for Evidence-based Medicine. Grades of recommendation are adapted from the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system.