Table 1.
Levels of evidence according to the study design[3]
| Level of evidence | Description |
| Type I | Evidence obtained at least from one well-designed, randomized, controlled1 trial or from a systematic review of randomized clinical studies |
| Type II | II-1 Evidence obtained from non-randomized, prospective, controlled1 studies |
| II-2 Evidence obtained from cohort observational studies2 or case-control studies, preferably multi-centric | |
| II-3 Evidence obtained from case series | |
| Type III | Opinion of authorities on the subject matter based on expertise, expert committees, case reports, pathophysiological studies or basic science studies |
1
A controlled study is a study where the intervention is managed by the researcher;
2
An observational study is a study where the intervention is not controlled by the researcher.