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The type of question will often dictate the best study design to address the question. In the absence of the best study design, move down the hierarchy of evidence:
| Clinical Question Type | Study Design |
|---|---|
| Clinical Examination | Prospective, blind comparison to gold / reference standard |
| Diagnostic Testing or Screening | Prospective, blind comparison to gold / reference standard |
| Prognosis | Cohort Study > Case Control Study > Case Series |
| Therapy | Randomized Controlled Trial (RCT) |
| Prevention | RCT > Cohort Study > Case Control Study > Case Series |
| Etiology / Harm | RCT* > Cohort Study > Case Control Study > Case Series |
| Cost | Economic analysis |
*it is not always ethical to randomize people to a known harmful exposure. However, some RCTs do contain information on adverse events, side effects, etc. that could be helpful in answering certain clinical questions regarding harms.