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Evidence Based Medicine Guide: Question Types

Question Types

Although recognizing your question's domain is not usually challenging, it is a crucial part of EBM process. Once you have established the question type, it's easier to:

  • Identify which research methodology will provide the best evidence to answer the question. The hierarchy of evidence differs depending on the question type.
  • Select the best resources to search for the evidence. The Cochrane Database of Systematic Reviews, for example, only addresses treatment and prevention questions.  ACP Journal Club reviews clinical research on questions of treatment and prevention, diagnosis, prognosis, etiology, quality improvement, and health economics, among others.
  • Select evidence filters in Medline/PubMed and other databases that will help narrow your search to results using appropriate research methods.

Identifying your question type will also assist you in appraising the evidence based on the appropriateness and rigor of the research methods described in a paper.

Common Clinical Questions

Question TypesEBM experts have identified four primary types of clinical questions. Once you have analyzed your question using the PICO format and written out the statement, identifying the question type (or domain) is straightforward. 

The following clinical questions are addressed in this tutorial:

Treatment (Therapy)

Questions about the effectiveness of interventions in improving outcomes in sick patients are the most frequently asked. Among the many treatments offered by physicians are medications, surgical procedures and counseling about lifestyles changes.


Questions about the effectiveness of an intervention or exposure in preventing morbidity and mortality are similar to treatment questions. When you assess preventive measures, though, it is particularly important to evaluate potential harms as well as benefits.


Questions about the ability of a test or procedure to differentiate between those with and without a condition or disease are common.

Prognosis (Natural History) 

Questions about the probable cause of a patient's disease or the likelihood that he or she will develop an illness occur in all age groups, and are especially important in pediatrics.

Etiology or Harm (Causation) 

Questions about the harmful effect of an intervention or exposure on a patient are more common than we would like.

*EBM practitioners are split on whether screening questions fit within the Diagnosis category or should constitute their own, distinct category.  In Evidence-Based Medicine, How to Practice and Teach EBM, Straus et al. are of the opinion that screening questions constitute a subcategory of Diagnosis questions, since screening questions involve, "making early diagnosis of pre-symptomatic disease among well individuals in the general public.1"

1. Straus SE, Richardson WS, Glasziou P, Haynes RB. Evidence-based medicine, how to practice and teach EBM. 3rd ed. Edinburgh; New York: Elsevier Churchill Livingstone; 2005.