Appendix 1

Levels of evidence and grade of recommendation

LevelStrength of evidence (Adapted from Muir Gray36)GradeGrade of recommendation (Cook et al37)
IStrong evidence from at least one systematic review of multiple well designed randomised controlled trialsASupported by level I evidence and therefore highly recommended.
IIStrong evidence from at least one properly designed randomised controlled trial of appropriate size.BSupported by level II evidence, and therefore recommended
IIIEvidence from well designed trials without randomisation, single group pre-post, cohort, time series or matched case-control studiesCSupported by level III, evidence. Several potential clinical actions might be considered appropriate.
IVEvidence from well designed non-experimental studies from more than one centre or research groupDSupported by level IV and V evidence. The consensus route would have to be adopted.
VaOpinions of respected authoritiesD
VbClinical evidence, descriptive studies or reports of expert committeesD