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P I C O: Formulate an Answerable Question

The ‘P I C O’ principle

Questions often spring to mind in a form that makes finding answers in the medical literature a challenge. Dissecting the question into its component parts and restructuring it so that it is easy to find the answers is an essential first step in Evidence Based MedicineGlossary link image (EBM). Many questions can be divided into 4 parts:


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Many clinical or research questions can be divided into these four components, which we call ‘P I C O’. Try to use all four parts of the question, if possible.

  P     Population/patient
 I     Intervention/indicator
  C     Comparator/control
  O     Outcome

Different types of questions

The most common type of clinical question is about how to treat a disease or condition. In Evidence Based Medicine (EBM), treatments and therapies are called ‘interventions’ and such questions are questions of INTERVENTION.

Not all research questions are about interventions. Other types of questions may arise:

  1. What causes the problem? AETIOLOGY, RISK FACTORS
  2. What is the frequency of the problem? FREQUENCY
  3. Does this person have the problem? DIAGNOSIS
  4. Who will get the problem? PROGNOSIS, PREDICTION

In each case the P I C O method can be used to formulate the question, as shown in the following examples. You can use the same approach to research qualitative questions about health issues of a more general nature (i.e. PHENOMENA). In this case, the question will consist of ‘P’ and ‘O’ only.

The studies that you will need to find in the course of your work will be different for each type of question and we will discuss this further in the next section.


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