Appendix A: Grading scheme

Appendix A: Grading scheme

The recommendation grading scheme and hierarchy of evidence used in this guideline are adapted from the Scottish Intercollegiate Guidelines Network (SIGN 50: A guideline developers' handbook), and summarised in the tables below.

Recommendation grade

Evidence

A

At least one meta-analysis, systematic review, or randomised controlled trial (RCT) rated as 1++ (see table on page 17), and directly applicable to the target population, or

A systematic review of RCTs 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+, or

Formal consensus

D (GPP)

A good practice point (GPP) is a recommendation for best practice based on the clinical experience of the Guideline Development Group

Level of evidence

Type of evidence

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 of RCTs, or RCTs with a low risk of bias

1

Meta-analyses, systematic reviews of RCTs, or RCTs with a high risk of bias

2++

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

3

Non-analytic studies (for example, case reports, case series)

4

Expert opinion, formal consensus