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Evidence-Based Practice: PICO and SPIDER


The PICO concept is commonly used to formulate the clinical question.

It is especially useful for questions that are about a therapy or intervention. PICO is commonly used when one intervention is being compared with another, or with no intervention at all.

Each of the 4 letters identifies a key concept that needs to be in research articles that will answer 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? This might be: no intervention.
O Outcome What is the anticipated or hoped-for outcome?

Another acronym that is sometimes used is PICOTT. The extra letters are for:

T Type of Question You can have questions of different types. They can be categorised as a diagnosis, prognosis, therapy, aetiology/harm, or prevention question.
T Type of Study This asks what study design would best answer the question: randomised controlled trial; cohort study; case controlled studycase series; case series; case report etc.

PICO Examples


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

"I work in an aged care facility where urinary tract infections are a common problem. I've heard that cranberry juice can help prevent UTIs. I wonder if there's any evidence for that and whether it might help our patients?"

P      Patients in aged care homes

I       Cranberry juice

C      No intervention (status quo)

O      Prevention of UTIs.



Here is a non-health example:

"I conduct Library induction classes for new students in an academic library. I wonder if playing music during the class would improve their retention of information and their experience of using the library."

P      First year students at an academic library attending face-to-face induction classes

I       Playing background music in the classroom

C      No intervention (status quo)

O      Increased retention of information and improved student comfort with the library.


The SPIDER tool can be used when dealing with qualitative research questions, that is, when the research is about attitudes and experiences rather than scientifically measurable data. It focuses less on the intervention and more on the design of the study, and deals with "samples" rather than a "patient" or "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 The measurement of outcome might be subjective and not necessarily empirical
R Research Type Qualitative, or quantitative, or mixed?

Research questions framed using the SPIDER tool tend to begin with "What are the experiences of ...?"

SPIDER Example

"What are the experiences of first year university students in using their library?"

S      First year university students

PI     Library use

D      Survey

E      Experiences (of using the Library)

R      Qualitative