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Evidence-Based Public Health: Forming a Question

Asking the Right Question with the 5 A's

The Five A’s of the Evidence Cycle

Incorporating best evidence into public health requires a systematic approach. A clear series of steps known as the Evidence Cycle can provide an excellent paradigm to guide you through this process. It involves knowing the right question to ask, turning that question into a good search, knowing the best place to look, finding what is available and then using the evidence you find in the care of your patient population. Use the "5 A's" as a step-by-step guide to locate best evidence.

  1. Assess
    • Identify the public health problem. What is it you want to know?
  2. Ask
    • Use the PICO formula to create a good question:
      • P=PATIENT – Who is your patient population?
      • I=INTERVENTION – What type of intervention are you trying to assess?  An educational intervention, a prevention initiative such as immunization, a policy change?
      • C=COMPARISON – Is there a control? Placebo? A "gold standard"?
      • O=OUTCOME – What do you hope to accomplish? Better/best prevention method(s)? Decreased mortality?
    • A good PICO might read "What is best/most cost-effective prevention method for cervical cancer in low-resource countries?"
  3. Acquire
    • Use your PICO formula to search for good evidence. Start your search using only two to three terms - you can always add more. Use the information resources on the EBM home page as a starting point.
  4. Appraise
    • What have you found? Where did you find it? Are the results significant to your patient population? How strong is the evidence? Are there any confounding variables such as bias present?
  5. Apply
    • Now apply and discuss the evidence you have found with your patient population.


A well-formed clinical question covers the following areas (PICO):

  •          Patient or population or problem
  •          Intervention or exposure or prognostic factor
  •          Comparison (not always included)
  •          Outcome

 Sample Questions:


Patient/Population/ Problem

Intervention/Exposure/ Prognostic Factor



Example 1

A group of children come down with measles. The parents of these kids are concerned about the potential health risks of vaccinations and have decided not to vaccinate any of their kids. You need to develop an intervention that increases the likelihood that this group will vaccinate their kids.

Children with measles

Program to increase vaccinations             

 Group not exposed

Does the exposed group have an increased rate of vaccinations compared to the non-exposed group? Is there a decreased rate of measles among the children of parents exposed to the intervention?

Example 2

There is a section of town which has a high prevalence rate of obesity and diabetes. There are many churches in that area so you decide to work with the churches to develop a series of interventions to reduce both obesity and diabetes. One of the programs will target foods served at church-sponsored events which are mostly pot-luck.

Members of a group of churches in an area of town

Program designed to improve types of foods served at church-sponsored

Goods served before the intervention  

Are more nutritious foods served at church-sponsored events after the intervention?

PICO Templates and Worksheets

Some of these PICO templates and worksheets were originally produced for other EBPH education programs and available for educational reuse.

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