As we saw on the previous page, the first step in the evidence-based practice process is to formulate a clinical question.

The clinical question should be relevant to the patient or the problem and formulated in such a way as to help with the search for an answer. Using a framework such as PICO or SPIDER can help you to work out the key elements of your question and know which concepts to combine in your literature searching.

There are many other frameworks that can be used for different types of questions. You should use the framework that best suits your type of question.

See our Systematic Review Guide - Identifying an answerable question for more detailed information.


The PICO framework is commonly used to formulate the clinical question. Each of the 4 letters identifies a key component of the question:

P Patient/Population/Problem Start with the patient, or group of patients, or problem.
I Intervention What is the proposed intervention?
C Comparison What is the main alternative, to compare with the intervention? (May be just the status quo)
O Outcome What is the anticipated or hoped-for outcome?

PICO is commonly used when one intervention is being compared with another, or with no intervention at all.

Sometimes this is expanded to PICOTT, which adds on:. The extra letters are for:

T        Type of  Question    - Such as a diagnosis, prognosis, therapy, aetiology/harm, or prevention question

T        Type of Study            - Includes the study design that would best answer the question: randomised controlled trial; cohort study; case controlled study; case series; case series; case report etc. See also Levels of Evidence.

PICO Example

Here is an example of a clinical problem formulated using PICO:

"Among women 50-74 years of age who are overdue by at least 12 months for a mammogram, does a telephone counselling call addressing personal barriers improve mammogram attendance?"

P Women aged 50-74 who are at least 12 months overdue for a screening mammogram
I Telephone counselling call
C Usual care e.g., reminder letter sent if women do not make appointment at annual wellness visit.
O Improved mammogram attendance

This example is adapted from:

McKenzee, J. K. (2019). Improving mammography adherence in the primary care setting. University of Northern Colorado.


The SPIDER tool can be used when dealing with qualitative research questions, that is, when the research is about attitudes and experiences rather than quantitatively measurable data. It focuses less on the intervention and more on the design of the study, and deals with "samples" rather than "populations".

S Sample The group of participants in qualitative research
PI Phenomenon of Interest The how and why of behaviours and experiences
D Design How the study was devised and conducted
E Evaluation Measurement of outcome might be subjective and not necessarily empirical
R Research Type Qualitative, or quantitative, or mixed?

Spider Example

Using the same example as in the PICO question, what if you were more interested in a qualitative study of the problem?

S Sample Women aged 50-74 who are overdue for a screening mammogram
PI Phenomenon of Interest Barriers to adhering to regular mammograms
D Design Survey
E Evaluation Experiences of barriers
R Research Type Qualitative

Now your clinical research question could be structured this way:

What barriers do women who fail to attend regular mammogram screening experience?

Again, notice that the phrasing of the question is now clear, and so is a much better start for your searching. You'll also notice that the final question formulated is very different to the one produced using the PICO strategy. You should use the strategy best suited for your chosen Clinical Question.

Further Reading

Evidence-Based Medicine in Practice

Professor Paul Glasziou from the University of Oxford's Centre for Evidence-Based Medicine (CEBM) talks about forming a PICO question.

Evidence-Based Practice: Step 1: Ask the Question (PICO)

Includes information on the different types of questions. (From the Medical University of North Carolina Libraries)

Evidence-Based Practice: What Type of Question

Information on PICO and SPIDER but also on other ways of structuring a research or clinical question. (From the University of Notre Dame Library, Australia)

Beyond PICO: the SPIDER tool for qualitative evidence synthesis

This article looks at using PICO and SPIDER as tools to help in literature searching.

Cooke, A., Smith, D., & Booth, A. (2012). Beyond PICO: The SPIDER tool for qualitative evidence synthesis. Qualitative Health Research, 22(10), 1435-1443. doi:10.1177/1049732312452938