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Formulating a Question (PICO)

Clinical questions usually have four components, termed PICO(TT). PICO is a formula or outline to help you both identify your question, and to facilitate your literature research.

P = patient or population of interest. (e.g. age, gender, ethnicity of person or population)
I  = intervention or interest (e.g. exposure, diagnostic test, prognostic factor, therapy or patient perception, etc.)
= comparison intervention or group
= outcome - either patient-oriented outcomes (things the patient cares about such as cost, time, morbidity,etc.) or disease-oriented outcomes (etiology, pathophysiology, etc.) 

= time Frame of intervention or observation (this is not always included)
(Sometimes an additional is added for type of question or study) 


When it comes time to search, break your question apart by PICO. Search by combining the separate components with AND. For more information on searching with AND (and other searching tools) see the Database Search Tips page of this guide. 

Example of a clinical question using PICO:
patients 65 years and older (P), does the use of an influenza vaccine (I) reduce the future risk of pneumonia (O) compared with patients who have not received the vaccine? (C)

Example of a search using the above PICO question:
(elder OR elderly) AND "influenza vaccine" AND pneumonia
(NOTE: This is just an example. A lot more can be done to this search - it is just a start.)

PICO video

The first part of this video defines and explains PICO.
The second part discusses how to use PICO to facilitate your literature search.

Types of Evidence

Where and how you begin your search will be affected by the type of data you need to answer your clinical question. Some types of sources are listed below. Unless otherwise noted, the best place to usually find these types of sources are in library databases such as PubMed, CINAHL, WoS, TRIP, etc. - see Search and Refine box below.

  • Randomized Controlled Studies  
    "A study in which the participants are assigned by chance to separate groups; neither the researchers nor the participants can choose which group." (PubMed Health Glossary) 

  • Quantitative studies 
    "Research that involves the collection of data in numeric form and emphasizes precise measurement of variables; often conducted in the form of rigorously controlled studies." (1)

Some types are considered "pre-filtered evidence," since they are the result of previous researchers/experts synthesizing the available research. These resources are helpful because the literature has been reviewed and evaluated by experts to provide an answer to a clinical question. 

  • Integrative Reviews
    "Scholarly papers that offer generalizations about substantive issues based on a set of relevant studies. They synthesize published studies and articles to find answers to questions of interest." (2)
  • Meta-analysis
    "A combination of the results of studies into a measurable format that statistically estimates the effects on proposed interventions and then critically reviews them to minimize bias. It is different from an integrative review in that it includes works that are similar or identical so that a statistical comparison can be made." (2)  
  • Systematic reviews
    Not literature reviews but reviews of actual research studies that address specific clinical questions. Conducted by experts who:
    1. establish selection criteria for studies that will be selected for inclusion in the review
    2. locate relevant studies
    3. critically appraise he methodological qualities of the study (strengths and weaknesses)
    4. summarize the data from the studies
    5. recommend implications for practice and further research 
  • Guidelines (In addition to databases, these can be found on government and organizational websites.)
    Information in guidelines is usually based on exhaustive systematic reviews of the relevant empirical literature coupled with expert opinion. They are created by specialty associations, professional societies, or governmental agencies that develop recommendations about a specific topic to guide clinical practice decisions. (3)

(1) Melnyk, Bernadette Mazurek and Ellen Fineout-Overholt. Evidence-based practice in nursing and healthcare. Philadelphia :; Lippincott Williams & Wilkins, 2005.
(2) Godshall, Maryann. Fast Facts for Evidence-Based Practice: Implementing EBP in a Nutshell. New York: Springer Pub. Co, 2010.
Fonteyn ME. "Teaching advanced practice nursing students how to use the Internet to support an evidence-based clinical practice." ACN CLIN ISSUES ADV PRACT ACUTE CRIT CARE, 2001 Nov; 12(4): 509-19

Evidence Pyramid

There are many examples of Evidence Pyramids, but they all follow the above system of hierarchy somewhat. The below pyramid was put together from a variety of them. The quality of evidence increases as you move up the pyramid. It is important to remember that the quality of evidence relies on the quality of the information you are looking at! A poorly done meta-anlaysis is not quality information. It is critical that you evaluate the evidence you are looking at. 


Due to the variability in quality as well as the nature of Systematic Reviews and Meta-Analyses, a new type of pyramid has been proposed.

The proposed new evidence-based medicine pyramid. (A) The traditional pyramid. (B) Revising the pyramid: (1) lines separating the study designs become wavy (Grading of Recommendations Assessment, Development and Evaluation), (2) systematic reviews are ‘chopped off’ the pyramid. (C) The revised pyramid: systematic reviews are a lens through which evidence is viewed (applied).


Databases for Evidence Based Practice/Medicine

Sources of evidence-based literature can be found in databases including those listed below. Most of these databases have limiters that allow you to focus on specific types of trials or pre-filtered evidence. 

*Depending on the type and amount of information you need, it is likely you will need to search more than one database/resource.* 

Begin your search with a few relevant keywords and adjust your search - the words, combinations, limits, which database you use - throughout. See the "Database Search Tips" tab for assistance.

You may also want to explore Web of Science and other library database list