| Level | Study design | Strength |
|---|---|---|
| I | Randomized controlled trials (RCTs) or meta-analyses of RCTs | High |
| II | Prospective cohort studies, lesser RCTs | Moderate–high |
| III | Case–control or retrospective cohort studies | Moderate |
| IV | Case series or descriptive studies | Low–moderate |
| V | Case reports, expert opinion, pathophysiologic reasoning | Low |