Table 1.

Summary of level of evidence and strength of recommendation classification according to the GRADE methodology.

Level of evidence
Grade	Definition	Letter
High	We are very confident that the true effect lies close to that of the estimate of the effect.	A
Moderate	We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different	B
Low	Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect.	C
Very low	We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect	D
Strength of recommendation
Grade	Definition	Number
Strong for an intervention	“Clinicians must…”	1+
Discretionary for an intervention	“Clinicians probably should…”	2+
Discretionary against an intervention	“Clinicians probably should not…”	2−
Strong against an intervention	“Clinicians must not…”	1−