SIGN Guidelines: SIGN-50 – A guideline developer’s handbook (2019 edition)
| Level |
Definition |
| 1++ |
High quality meta-analyses, systematic reviews of RCTs, or RCTs with a very low risk of bias |
| 1+ |
Well-conducted meta-analyses, systematic reviews, or RCTs with a low risk of bias |
| 1- |
Meta-analyses, systematic reviews, or RCTs with a high risk of bias |
| 2++ |
High quality systematic reviews of case control or cohort or studies 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 |
Non-analytic studies, e.g. case reports, case series |
| 4 |
Expert opinion |
SIGN Guidelines: Annex B: Key to evidence statements and grades of recommendations (Historical only, 1999-2012 system)
| Grade |
Recommendation |
| A. |
At least one meta-analysis, systematic review, or RCT 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+
A body of evidence including studies rated as 2+, directly applicable to the target population and demonstrating overall consistency of results; or |
| C. |
Extrapolated evidence from studies rated as 2++
Evidence level 3 or 4; or |
| D. |
Extrapolated evidence from studies rated as 2+ |
Good practice points
Recommended best practice based on the clinical experience of the guideline development group |