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Systematic Review

Are you considering developing a systematic review on a topic, but unsure where to start? This guide will help you to get started.

Step 1: What is the question?

Clarify your clinical question: 

Users' Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice, 3rd ed, 2015 - Framing Clinical Questions: PICO

  • Patients or population: Who are the relevant patients?
  • Intervention(s) or Exposure(s): For example, diagnostic tests, foods, drugs, surgical procedures, time, or risk factors. What are the management strategies we are interested in comparing or the potentially harmful exposures about which we are concerned?
  • Comparator: For issues of therapy, prevention, or harm, there will always be both an experimental intervention or putative harmful exposure and a control, alternative, or comparison intervention or state to which it is compared.
  • Outcome: What are the patient-relevant consequences of the exposures in which we are interested? We may also be interested in the consequences to society, including cost or resource use. It may also be important to specify the period of interest.

Using the PICO Model to frame your research question can often assist in planning your search strategy. The Cochrane Handbook for Systematic Reviews of Interventions (2011) includes the following factors to consider when developing your question using PICO:


Patient, Population or Problem

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?

Interventions and Comparisons

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.

Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from

Please note that PICO is only one of many frameworks.  Also that you will not search every term in your question.