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Systematic Reviews

Question Frameworks

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When doing a systematic review, having a research question framework can help you to identify key concepts of your research and facilitate the process of article selection for inclusion in the systematic review.

Framework for quantitative studies

- PICO is commonly used to frame quantitative systematic review questions and contains the following elements:

  • P Patient, Problem or Population: demographic factors of your patient/population such as age, gender, ethnicity, socioeconomic status, etc.
  • I Intervention: which main intervention, prognostic factor, or exposure are you considering?
  • C Comparison or Control: what is the main alternative to compare with the intervention?
  • O Outcome: what do you want to accomplish, measure, improve or affect? (ex: reduce mortality, improve water access, etc.). Outcomes should be measurable by indicators (e.g. quality of life, etc.)

Example: What are the socioeconomic and environmental effects (outcome) of the program "Payment for Environmental Services" (intervention) in low and middle income countries (population)? In this case, one can compare groups that receive the intervention with groups without intervention (comparison).

Frameworks for qualitative research

- PICO for Qualitative Studies

As the PICO tool does not  always accommodate terms relating to qualitative research or specific qualitative designs, it has often been modified in practice to “PICOS” where the “S” refers to the Study design, thus limiting the number of irrelevant articles.   

If we use the previous example (the effects of the program "payment for environmental services"), where mixed research methods are employed, the study design (focus groups, interviews, observations, etc.) can be useful to find studies.


The SPIDER question format was adapted from the PICO tool to search for qualitative and mixed-methods research. Questions based on this format identify the following concepts:

  • Sample
  • Phenomenon of interest
  • Design
  • Evaluation
  • Research type

Example: What are the experiences (evaluation) of young parents (sample) of attending antenatal education (Phenomenon of Interest)? Design: Interviews, surveys. Research Type: the type of qualitative research (phenomenology, ethnography, grounded theory, case study).


According to a comparison study between PICO, PICOS and SPIDER “the recommendations for practice are to use the PICO tool for a fully comprehensive search but the PICOS tool where time and resources are limited. The SPIDER tool would not be recommended due to the risk of not identifying relevant papers, but has potential due to its greater specificity”.