Table 1 Scale of quality of evidence for a therapy recommendation

1a:

Systematic reviews (with homogeneity) of randomized controlled trials

1b:

Individual randomized controlled trials (with narrow confidence interval)

1c:

All or none randomized controlled trials

2a:

Systematic reviews (with homogeneity) of cohort studies

2b:

Individual cohort study or low quality randomized controlled trials (e.g. < 80% follow-up)

2c:

“Outcomes” research; ecological studies

3a:

Systematic review (with homogeneity) of case-control studies

3b:

Individual case-control study

4:

Case-series (and poor quality cohort and case-control studies)

5:

Expert opinion without explicit critical appraisal or based on physiology, bench research or “first principles”