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PICO Searching

Helpful guide to get you started on your clinical question literature searches

What is the PICO Method?

The PICO Method is a way to not only help you form specific, relevant clinical questions, but is also a way to formulate a database search strategy. The PICO mnemonic helps you to identify the key concepts that need to be in articles in order to answer your clinical question.

The PICO Elements are as follows:

P: Population, Problem or Patient                                    Description of specific subset of patients you are researching. How would you describe others who belong to the same group as your specific patient?
I: Intervention, Prognostic Factor or Exposure What is the main intervention or exposure I am interested in exploring?
C: Comparison What, if anything, am I comparing my main intervention against?
O: Outcome What am I trying to measure, improve or affect?


Types of Clinical Questions

There are 2 main types of clinical question: Background Questions and Foreground Questions.

  • Concern well-documented or well-known knowledge in the field
  • Generally have 2 parts: ​​
    • A question root (who, what, when, where, how, why) and
    • A disorder, test, treatment, or other aspect of health care
  • Words to look out for: normal, standard, average, typical, usual, etc.
  • Often, these questions can best be answered by using a handbook, textbook, encyclopedia, clinical app or sometimes tables, charts or standard calculations
  • Are highly specific knowledge questions that affect clinical decisions
  • They include a broad range of biologic, psychological, and sociologic issues
  • Generally answered by searching the primary medical literature (databases)
  • These are the questions we PICO

Foreground Question Domains

Foreground Questions can further be classified into their DOMAIN - what aspect of medical care the question is investigating. Different types of research study are better suited to answering questions in different domains. ALL foreground question domains are best answered by well-done Meta-Analysis, Systematic Reviews or Evidence-Based Practice Guidelines.

The following table lists the question domain and the best single study research design for answering a question domain.

Domain Single Study Types


Randomized Controlled Trials (RCTs)


Randomized Controlled Trials (RCTs) > cohort > case control > case series


Cohort > case control > case series


Cohort (follow-up) > case control > case series


Prospective, blind comparison to gold standard

Hierarchy of Evidence

Knowing that some study designs are better than others for answering clinical questions, we can think of evidence being arranged in a hierarchy. The hierarchy is pyramid-shaped because as the study design becomes more rigorous, fewer of these types of studies are created. The most robust evidence, meta-analysis and systematic review, are at the very top of the evidence pyramid, no matter which pyramid scheme you choose to use. (Some pyramids include secondary sources, some include guidelines, etc.)

Here's an example of an evidence pyramid, created by the Dahlgren Memorial Library at Georgetown, that only includes primary research study types:

Pyramid of Evidence based medicine levels