Table 1

 Evidence hierarchy (modified from Shekelle et al11)

Category of evidenceType of study
RCT, randomised controlled trial.
IaMeta-analysis of RCTs or >1 RCT with similar results
IiaControlled study without randomisation
IIbQuasi experimental study
IIINon-experimental descriptive studies such as comparative, correlation and case–control studies
IVExpert committee reports or opinion or clinical experience of respective authorities, or both