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Levels of evidence10
| Level I | Systematic review/meta-analysis |
| Level II | One or more randomized clinical trials |
| Level III | Nonrandomized controlled trials |
| Level IV | Analytic epidemiology (cohort studies and case-control studies) |
| Level V | Descriptive study (case reports and case-series studies) |
| Level VI | Opinions of expert panels and individual experts not based on patient’s data |
