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Hierarchy of Evidence

Types of Questions

Common Types of Questions:

  • Therapy: how to select treatment to offer patients that do more good than harm and that are worth the efforts and costs of using them.
  • Diagnosis: how to select and interpret diagnostic tests in order to confirm or exclude a diagnosis, based on considering their specificity, sensitivity, likelihood ratios, expense, safety, etc.
  • Prognosis: how to estimate the patient's likely clinical course over time and anticipate likely complications of disease.
  • Etiology/Harm: how to identify causes for disease.
  • Prevention: how to reduce the chance of disease by identifying and modifying risk factors and how to diagnose early by screening.

The type of question is important and can help lead you to the best study design. To limit your search to a specific study design, use the database's filters/limits or add keywords to your search (e.g., lung cancer AND cohort).

Type of Question  Best Type of Study
   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

Study Design Info From Other Institutions