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Levels of evidence
| Level | Therapeutic studies | Prognostic studies |
|---|---|---|
| I | High-quality randomized controlled trial | High-quality prospective study |
| II | Lesser-quality randomized controlled trial | Retrospective study |
| Prospective comparative study | Lesser-quality prospective study | |
| III | Retrospective comparative study | Case–control study |
| IV | Case series | Case series |
| V | Expert opinion | Expert opinion |
