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Evidence-Based Pyramid

The Evidence-Based Pyramid is divided into levels to indicate:

  • the volume of information at each level
  • that different study types have differing rigor, quality and reliability.

As we ascend the pyramid, the quality of evidence increases. However, study design always has an impact. A well designed cohort study for example, is likely to provide better evidence than a poorly designed randomised controlled trial (RCT). The quality of each individual study still needs to be critically appraised. 

 
Best study type to answer different clinical questions

As demonstrated by the pyramid above, not all evidence has the same power. In addition, different types of questions are best answered by particular study types (see below).

  • Each of the five types of clinical questions are best answered by the following evidence types:
    • Therapy - determining the effect of interventions = RCT, systematic review, meta-analysis.
    • Prognosis - likely outcome for a patient population = RCT, cohort study, case-control study.
    • Harm - outcomes from an activity of exposure = RCT, cohort study, case-control study.
    • Diagnosis - accuracy of diagnostic tests = Cross-sectional analytic study, blind comparison to a gold standard.
    • Prevention - reducing chance of disease by identifying risk factors = RCT, systematic review.
 
A note about systematic reviews

  1. As you can see in the EBP pyramid, systematic reviews are the highest level of evidence. Most researchers want to find a systematic review to answer their clinical question, as systematic reviews synthesise evidence from all existing studies in a particular area to provide a thorough analysis of the collated results, strengths and weaknesses. 

    Systematic reviews may or may not include a meta-analysis to summarise and analyse the statistical results from included studies. Researchers should note that systematic reviews have a very different design to narrative reviews, which are only useful for background information as they are designed as opinion reviews with selective illustrations from a literature search.

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