Table 7

Grading of Evidence Using the SIGN Grading System

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

Lawn et al. BMC Pregnancy and Childbirth 2009 9(Suppl 1):S2   doi:10.1186/1471-2393-9-S1-S2