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Systematic Review Overview: 1. Formulate a Research Question

Introduction to the 8 elements that encompass a systematic review
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Step 1. Formulate a Research Question

The strength of a systematic review lies in the presentation of a clear, answerable research question. This question will drive the direction of the systematic review, help identify the terms to be used in the literature search, demonstrate the relationship between the terms, and identify the outcomes being sought.

When developing a research question it is important to remember that it must be posed as a hypothesis and can be answered.

For the major categories of medical questions, a model, or framework, has been designed to assist researchers in developing their question. This is known as the PICO model. This PICO model is taught in Evidence-Based Medicine and Clinical Epidemiology programs as a means of clarifying and delineating the question.

The PICO Model:

P – the patient, the population, or the problem of interest
I – the intervention
C – the comparison (if one is required)
O – the outcome(s) being investigated.

Occasionally, the PICO model may be amended with an additional category: M/S – representing the methodology/study type(s) that are the most suitable for answering the question.


Here is an example of a completed PICO model arising from a clinical scenario.

There is an elderly patient requiring liver resection for liver cancer. He is at high risk for pulmonary embolism. Either heparin or warfarin could be used as anticoagulants to prevent pulmonary embolism. Which drug therapy should be used?

P – patient at risk for pulmonary embolism
I – heparin
C – warfarin
O – drug therapy effectiveness
M/S – randomized controlled trials

Driven by the completed PICO model, the question becomes:

In patients at risk for pulmonary embolism, is heparin or warfarin a more effective therapy in preventing pulmonary embolism?

To locate the better evidence, the search would be limited to randomized controlled trials.

As a result of the PICO model, the question and terms to be searched are clear:

  • Pulmonary embolism
  • Heparin
  • Warfarin
  • Randomized controlled trials

Next, the relationships between the terms need to be established. In this example, we need to find literature that contains all of our concepts. Therefore we would search each of the terms from the PICO model and combine them with AND.

Pulmonary embolism AND Heparin AND Warfarin AND Randomized Controlled Trials

Well built questions are critical to a systematic review. They provide the focus for the research and determine the final criteria for the review.