Table 1

 Grades of scientific evidence supporting the recommendations formulated in the Maastricht III Consensus Report

Grade of recommendationEvidence levelType of studies
A11aSystematic review of randomised controlled trials (RCT) of good methodological quality and with homogeneity
1bIndividual RCT with narrow confidence interval
1cNon-controlled studies
B22aSystematic review of cohort studies (with homogeneity)
2bIndividual cohort studies (including low quality RCT, eg <80% follow-up)
2cNon-controlled cohort studies/ecological studies
33aSystematic review of case-control studies (with homogeneity)
3bIndividual case-control studies
C4Case series/poor quality cohort or case-control studies
D5Expert opinion without explicit critical appraisal or based on physiology, bench research or “first principles”