Table 1

Categorisation of the quality of evidence

Quality of evidenceDescription
IEvidence obtained from at least one properly randomised, controlled trial
II-1Evidence obtained from well-designed controlled trials without randomisation
II-2Evidence obtained from well-designed cohort or case–control analytical studies, preferably from more than one centre or research group
II-3Evidence obtained from comparison between times and places with or without the intervention, or dramatic results in uncontrolled experiments
IIIOpinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees