Table 1.

Gradation of evidence and recommendations as an expression of the degree of certainty/uncertainty of the knowledge base for the respective recommendations

Level of evidence	According to OCEBM 2011	Symbol
Evidence level 1	Systematic review of randomized controlled studies	1
Evidence level 2	Randomized controlled study or observational study with dramatic effect	2
Evidence level 3	non-randomized controlled cohort study	3
Evidence level 4	case series, case-control studies, or historically controlled studies	4
Evidence level 5	Pathophysiological-mechanistic arguments	5

Quality of evidence	In accordance to GRADE
High quality	Further research is unlikely to affect our confidence in the estimation of the (therapeutic) effect
Medium quality	Further research is likely to affect our confidence in the estimation of the (therapeutic) effect and may alter the estimate
Low quality	Further research will most likely influence our confidence in the estimation of the (therapeutic) effect and will probably change the estimate
Very low quality	Any estimation of the (therapy) effect is very uncertain

Recommendation grade	Wording	Symbol
Strong recommendation	Ought to/ought not to	A/A–
Recommendation	Should/should not	B/B−
Therapy option	Can be considered	0