Skip to Main Content

Systematic Reviews: Formulate the question

A guide to assist staff and students undertaking systematic reviews

Formulate the question

The systematic review question is formulated a and tested during the scoping phase. There are many mnemonics available to assist you to formulate a search strategy based on the type of review you are undertaking and the kind of question you are asking.
A standard formula for structuring the review question is PICO(S) for quantitative questions and SPIDER for qualitative questions.

These mnemonics can be used to construct your research question and break down your search strategy. Remember that equal emphasis may not be put on each part of the mnemonic, and will largely depend on the topic of your systematic review.

The PICO structure can be used to help you put together a search strategy and formulate the question:

      Participants, Patient or Population       

      Intervention(s) (therapy, treatment, etc.)

      Comparison (other intervention or treatment, no treatment, etc. It's not always necessary to have a comparison group)


      Study design (consider which study design will best answer the question)

In some cases the review question may also include the Study Design (PICOS). This is outlined in the Centre for Reviews and Dissemination, University of York, guide “Systematic reviews: CRD's guidance for undertaking reviews in health care”:

“The review question can be framed in terms of the population, intervention(s), comparator(s) and outcomes of the studies that will be included in the review. These elements of the review question, together with study design, will then be refined in order to determine the specific inclusion criteria that will be used when selecting studies for the review.”

"Not every review question will specify type of study design to be included". See Levels of Evidence page for hierarchy of study design


P:    Population or Problem of interest
:     Interest (The phenomena of Interest relates to a defined event, activity, experience or process)
:  Context (Context is the setting or distinct characteristics. Note: Context not comparator)

Two other mnemonics may also be used to create protocols for both qualitative and quantitative studies - SPICE and SPIDER

SPICE: Within social sciences research, SPICE may be more appropriate for formulating research questions:

S:  Setting
P:  Perspective
I:   Intervention
C:  Comparison
E:  Evaluation


SPIDER can be used for both qualitative and quantitative studies:

S:   Sample
Pl:  Phenomenon of Interest
D:   Design
E:   Evaluation
R:   Research Type