Type of Clinical Question
|
Suggested Level of Evidence
|
Therapy
|
RCT > cohort > case control > case series
|
Diagnosis
|
Prospective, blind comparison to a gold standard
|
Etiology/Harm
|
RCT > cohort > case control > case series
|
Prognosis
|
Cohort study > case control > case series
|
Prevention
|
RCT > cohort study > case control > case series
|
Clinical Exam
|
Prospective, blind comparison to gold standard
|
Cost
|
economic analysis
|
Questions of therapy, etiology, and prevention, which can best be answered by a RCT, can also be answered by a meta-analysis or systematic review.

The hierarchy of evidence is often presented as a pyramid, ranking study types based on their research methods, with systematic reviews and meta-analyses at the top, and expert opinion and anecdotal experience at the bottom.