Assignment of levels of evidence and strength of recommendations [9]

CategoryDescription
Level of evidence
Level ISystematic reviews, meta-analyses, randomized controlled trials.
Level IITwo-group studies, non-randomized (e.g., case-control or cohort studies).
Level IIIOne-group studies, non-randomized (e.g., pre-post studies, before-and-after designs).
Level IVDescriptive studies including variable analysis (e.g., single-subject designs, case series).
Level VCase reports and expert opinions, including narrative reviews, literature reviews, and consensus statements.
Grade of recommendation
Grade AConsistent level I studies.
Grade BConsistent level II or III studies, or extrapolations from level I studies.
Grade CLevel IV studies, or extrapolations from level II or III studies.
Grade DLevel V evidence or concerningly inconsistent or inconclusive studies at any level.
Strength of recommendation
StrongEvidence from studies with a low risk of bias.
ModerateEvidence from studies with a moderate risk of bias.
WeakEvidence from studies with a high risk of bias.

Reprinted with permission from [45]. © 2020 EAACI and John Wiley and Sons A/S