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Systematic Reviews

Developing Answerable Questions

A technique often used in health research for formulating a clinical question is the PICO Model.

Using PICO, a clinical question will have 4 elements – Patient, Intervention, Comparison and Outcome.

The Cochrane Handbook for Systematic Reviews of Interventions includes the following factors to consider when developing criteria for your PICO elements.

We have three resources which provide a PICO search interface (Library VPN Required for licensed resources)

Ovid MEDLINE PICO search  (must be on campus network)

Embase PICO Search (must be on campus network)

PubMed PICO search


  • How is the disease/condition defined?
  • What are the most important characteristics that describe the people?
  • Are there any relevant demographic factors (eg. age, sex, ethnicity)?
  • What is the setting (eg. hospital, community, etc)?
  • Who should make the diagnosis?
  • Are there any other types of people who should be excluded from the review (because they are likely to react to the intervention in a different way)?
  • How will studies involving only a subset of relevant participants be handled?
  • What are the experimental and control (comparator) interventions of interest?
  • Does the intervention have variations (eg. dosage/intensity, mode of delivery, personnel who deliver it, frequency of delivery, duration of delivery, timing of delivery)?
  • Are all variations to be included (for example is there a critical dose below which the intervention may not be clinically appropriate)?
  • How will trials including only part of the intervention be handled?
  • How will trials including the intervention of interest combined with another intervention (co-intervention) be handled?
  • Main outcomes, for inclusion in the ‘Summary of findings’ table, are those that are essential for decision-making, and should usually have an emphasis on patient-important outcomes.
  • Primary outcomes are the two or three outcomes from among the main outcomes that the review would be likely to be able to address if sufficient studies are identified, in order to reach a conclusion about the effects (beneficial and adverse) of the intervention(s).
  • Secondary outcomes include the remaining main outcomes (other than primary outcomes) plus additional outcomes useful for explaining effects.
  • Ensure that outcomes cover potential as well as actual adverse effects.
  • Consider outcomes relevant to all potential decision makers, including economic data.
  • Consider the type and timing of outcome measurements.