Table 1.
Levels of evidence according to the study design
| Level of evidence | Description |
| Type I | Evidence obtained from at least one well-designed, randomized, controlled1 trial or from a systematic review of randomized clinical studies |
| Type II | II-1 Evidence obtained from nonrandomized, prospective, controlled1 studies |
| II-2 Evidence obtained from cohort observational studies2 or case-control studies, preferably multicenter | |
| II-3 Evidence obtained from case series | |
| Type III | Opinions 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 in which the intervention is managed by the researcher;
2
An observational study is a study in which the intervention is not controlled by the researcher.