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Systematic Reviews & Evidence Synthesis Methods

A detailed, step-by-step guide to the first several stages of an evidence synthesis review.

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Developing a Research Question

Developing your research question is one of the most important steps in the evidence synthesis process. At this stage in the process, you and your team have identified a knowledge gap in your field and are aiming to answer a specific question:

  • If X is prescribed, then Y will happen to patients?

OR assess an intervention:

  • How does X affect Y?

OR synthesize the existing evidence

  • What is the nature of X? ​

​​Whatever your aim, formulating a clear, well-defined research question of appropriate scope is key to a successful evidence synthesis. The research question will be the foundation of your synthesis and from it your research team will identify 2-5 possible search concepts. These search concepts will later be used in step 5 to build your search strategy. 

Research Question Frameworks

Formulating a research question takes time and your team may go through different versions until settling on the right research question. To help formulate your research question, some research question frameworks are listed below (there are dozen of different types of these frameworks--(for a comprehensive, but concise, overview of the almost 40 different types of research question frameworks, see this review from BMJ Global Health: Rapid review of existing question formulation frameworks).

Think of these frameworks as you would for a house or building. A framework is there to provide support and to be a scaffold for the rest of the structure. In the same way, a research question framework can also help structure your evidence synthesis question.  Probably the most common framework is PICO:

PICO for Quantitative Studies

  • P       Population/Problem
  • I        Intervention/Exposure
  • C       Comparison
  • O      Outcome

Example: Is gabapentin (intervention), compared to placebo (comparison), effective in decreasing pain symptoms (outcome) in middle aged male amputees suffering phantom limb pain (population)?

While PICO is a helpful framework for clinical research questions, it may not be the best choice for other types of research questions, especially outside the health sciences. Here are a few others:

PICo for Qualitative Studies

  • P       Population/Problem
  • I         Phenomenon of Interest 
  • Co    Context

Example: What are the experiences (phenomenon of interest) of caregivers providing home based care to patients with Alzheimer's disease (population) in Australia (context)?


  • S   Setting
  • P   Perspective (for whom)
  • I    Intervention/Exposure
  • C   Comparison
  • E   Evaluation

Example: What are the benefits (evaluation) of a doula (intervention) for low income mothers (perspective) in the developed world (setting) compared to no support (comparison)?


  • S     Sample
  • PI    Phenomenon of Interest
  • D     Design
  • E     Evaluation
  • R     Study Type

Example: What are the experiences (evaluation) of women (sample) undergoing IVF treatment (phenomenon of interest) as assessed?

Design: questionnaire or survey or interview

Study Type: qualitative or mixed method

Inclusion/Exclusion Criteria

Inclusion and exclusion criteria are developed after a research question is finalized but before a search is carried out. They determine the limits for the evidence synthesis and are typically reported in the methods section of the publication. For unfamiliar or unclear concepts, a definition may be necessary to adequately describe the criterion for readers.



An image describing various inclusion and exclusion criteria for systematic reviews.

Image from The University of Melbourne Library


Other inclusion/exclusion criteria can include the sample size, method of sampling or availability of a relevant comparison group in the study. Where a single study is reported across multiple papers the findings from the papers may be merged or only the latest data may be included.

How a Librarian Can Help

Librarians can help you learn how to search for existing information on your topic. Finding existing reviews on your topic will inform the development of your research question, identify gaps, and confirm that you are not duplicating the efforts of previous reviews. Contact the Evidence Synthesis Library Team to learn more about developing a research question.

Video: Formulating a research question (4:43 minutes)