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Evidence-Based Medicine: Ask a Clinical Question

This is a libguide for praticing evidence-based medicine.

Type of questions

Clinical questions arise around the central issues involved in caring for patients. It is helpful to understand the category type of  the clinical question that you are asking. There are four fundamental types of clinical questions:

    1. Therapy: questions concerning the effectiveness of a treatment or preventative measure.

    2. Harm/Etiology:  questions concerning the likelihood of a therapeutic intervention to cause harm.

    3. Diagnosis: questions concerning the ability of a test to predict the likelihood of a disease.

    4. Prognosis Questions concerning the future course of a patient with a particular condition.

Why bother formulating questions clearly?

Well-formulated questions can help in many ways:

1. They help to focus on evidence that is directly relevant to patients’ clinical needs.

2. They help to focus on evidence that directly addresses clinicians or learners' knowledge needs.

3. They can suggest high-yield search strategies.

4. They suggest the forms that useful answers might take.

5. They can help to communicate more clearly with clinicians and faciliate education and learning.

Using PICOTS framework to form a well built clinical question

When well built, clinical questions usually have four components:

P: The patient situation, population, or problem of interest.
I: The main intervention, defined very broadly, including an exposure, a diagnostic test, a prognostic factor, a treatment, a patient  perception, and so forth.
C: A comparison intervention or exposure (also defined very broadly), if relevant.
O: The clinical outcome(s) of interest, including a time horizon, if relevant.

Besides standard PICO components, PICOTS framework is extremely useful and important for defining the key clinical questions and assessing whether a given study is applicable or not. T refers to Timing and S refers to Setting or sometimes Study Design.

T: Timing, i.e. the time it takes to demonstrate an outcome OR the period in which patients are observed.
S: Setting (e.g. ambulatory settings including primary, specialty care and inpatient settings) or sometimes Study Design.

Reference: Matchar DB. Introduction to the Methods Guide for Medical Test Reviews. AHRQ Publication No. 12-EHC073-EF. Chapter 1 of Methods Guide for Medical Test Reviews (AHRQ Publication No. 12-EHC017). Rockville, MD: Agency for Healthcare Research and Quality; June 2012.

PICO(T) Templates (McMaster University Health Sciences Library)

Example for Therapy question:

In ___[P]___,  do/does ___[I]___ result in ___[O]____ when compared with ___[C]___ over ___[T]____?

E.g.) In nursing home residents with osteoporosis, do hip protectors result in fewer injuries from slips, trips, and falls when compared with standard osteoporosis drug therapy over the course of their stay?


PICO Form (National Library of Medicine)

Finding a suitably designed study for your question type

Correctly identifying the type of question can help you to find appropriately designed study:

Most common type of  questions    Study design
Therapy                                              randomized controlled trial > cohort study
Harm/Etiology                                         cohort study > case control > case series
Diagnosis   prospective, blind comparison to a gold standard or cross-sectional
Prognosis cohort study > case control > case series