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HSWG Hierarchy of Evidence
| Validity of Evidence | What to Look For |
| ++++ (Best Evidence) | Randomized controlled trials |
| +++ | Non-randomized controlled trials |
| ++ | Well designed cohort or case-control analysis |
| + | Opinions of respected authorities, case reports, descriptive studies, reports of expert committees |
| No Evidence | Misrepresentation, fraud |
