Table 2.

Grade/strength of recommendation classification systems for included guidelines.^a

National Institute for Health and Care Excellence (NICE)
Strength of recommendations The wording used denotes the certainty with which the recommendation is made (the strength of the recommendation). Interventions that must (or must not) be used We usually use “must” or “must not” only if there is a legal duty to apply the recommendation. Occasionally, we use “must” (or “must not”) if the consequences of not following the recommendation could be extremely serious or potentially life threatening. Interventions that should (or should not) be used: a “strong” recommendation We use “offer” (and similar words such as “refer” or “advise”) when we are confident that, for the vast majority of patients, an intervention will do more good than harm and be cost-effective. Interventions that could be used We use “consider” when we are confident that an intervention will do more good than harm for most patients and be cost-effective, but other options may be similarly cost-effective. The choice of intervention, and whether or not to have the intervention at all, is more likely to depend on the patient’s values and preferences than for a strong recommendation.
Scottish Intercollegiate Guidelines Network (SIGN) and European Psychiatric Association
Levels of evidence 1++: High-quality meta-analyses, systematic reviews of randomized controlled trials, or randomized controlled trials with a very low risk of bias; 1+: Well-conducted meta-analyses, systematic reviews, or randomized controlled trials with a low risk of bias; 1: Meta-analyses, systematic reviews, or randomized controlled trials with a high risk of bias 2++: High-quality systematic reviews of case control or cohort studies or high-quality case control or cohort studies with a very low risk of confounding or bias and a high probability that the relationship is causal; 2+: Well-conducted case control or cohort studies with a low risk of confounding or bias and a moderate probability that the relationship is causal; 2: Case control or cohort studies with a high risk of confounding or bias and a significant risk that the relationship is not causal 3: Nonanalytic studies (e.g., case reports, case series) 4: Expert opinion Grades of recommendation A: At least one meta-analysis, systematic review, or randomized controlled trial rated as 1++ and directly applicable to the target population or a body of evidence consisting principally of studies rated as 1+, directly applicable to the target population, and demonstrating overall consistency of results B: A body of evidence including studies rated as 2++, directly applicable to the target population, and demonstrating overall consistency of results or extrapolated evidence from studies rated as 1++ or 1+ C: A body of evidence including studies rated as 2+, directly applicable to the target population, and demonstrating overall consistency of results or extrapolated evidence from studies rated as 2++ D: Evidence level 3 or 4 or extrapolated evidence from studies rated as 2+ Good Practice Point: recommended best practice based on the clinical experience of the guideline development group

^aThis is a condensed table; please see the Introduction and Methodology paper for full details.