Individual studies included in the guideline are formally assessed using the GRADE system1 with the quality of the body evidence rated, from ‘high’ (A) to ‘very low’ (D)
| Modify the initial quality of a body of evidence | ||||
|---|---|---|---|---|
| Study design | Initial quality of a body of evidence | Rate lower if | Rate higher if | Quality of body of evidence |
| Randomised controlled trials | High★★★★ | Risk of bias −1 Serious −2 Very serious | Large effect +1 Large +2 Very large | High (A)★★★★ |
| Inconsistency −1 Serious −2 Very serious | Dose response +1 Evidence of a gradient | Moderate (B)★★★ | ||
| Observational studies/qualitative studies | Low★★ | Indirectness −1 Serious −2 Very serious | All plausible residual confounding | |
| Imprecision −1 Serious −2 Very serious | +1 would reduce a demonstrated effect | Low (C)★★ | ||
| Publication bias −1 Likely −2 Very likely | +1 would suggest a spurious effect if no effect observed | Very low (D) ★ | ||