Table 7 Grading of Evidence Using the SIGN Grading System
From: 3.2 million stillbirths: epidemiology and overview of the evidence review
Assessment of individual studies | Grade |
|---|---|
High quality meta analysis, systematic review of randomized controlled trials (RCT), or RCT with very low risk of bias | 1++ |
Well-conducted meta analysis, systematic review of RCTs, or RCT with a low risk of bias | 1+ |
Meta analysis, systematic review of RCTs, or RCT with a high risk of bias | 1- |
High quality systematic reviews of case-control or cohort studies High quality case-control or cohort studies with a very low risk of confounding, bias, or chance and a high probability that the relationship is causal | 2++ |
Well conducted case control or cohort studies with a low risk of confounding, bias, or chance and a moderate probability that the relationship is causal | 2+ |
Case control or cohort studies with a high risk of confounding, bias, or chance and a significant risk that the relationship is not causal | 2- |
Non-analytic studies, e.g. case reports, case series | 3 |
Expert opinion | 4 |
Assessment of all evidence for each intervention | Grade |
At least 1 meta analysis, systematic review, or RCT rated as 1++, directly applicable to the target population; or a systematic review of RCTs or a body of evidence consisting primarily of studies rated as 1+, directly applicable to the target population and demonstrating consistent overall results | A |
Body of evidence including studies rated as 2++, directly applicable to the target population, and demonstrating consistent overall results; or extrapolated evidence from studies rated as 1++ or 1+ | B |
Body of evidence including studies rated as 2+, directly applicable to the target population and demonstrating consistent overall results; or extrapolated evidence from studies rated as 2++ | C |
Body of evidence 3 or 4; or extrapolated evidence from studies rated as 2+ | D |