Table 1 Levels of evidence for studies of therapeutic interventions from the Oxford Centre for Evidence-based Medicine (website title http://www.cebm.net/levels_of_evidence.asp) [14]
From: A systematic review of intravenous gamma globulin for therapy of acute myocarditis
Level | Study design | |
|---|---|---|
1 | A | Systematic review (with homogeneity) of randomized controlled trials |
| Â | B | Individual randomized controlled trial (with narrow confidence interval) |
| Â | C | All or none |
2 | A | Systematic review (with homogeneity) of cohort studies |
| Â | B | Individual cohort study (including low quality randomized controlled trial, e.g., < 80% follow-up) |
| Â | C | "Outcomes" research; ecological studies |
3 | A | Systematic review (with homogeneity) of case-control studies |
| Â | B | Individual case-control study |
4 | Â | Case series (and poor quality cohort and case-control studies) |
5 | Â | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" |