The Evidence Pyramid

Acquiring the most credible and relevant studies for a specific research question is the second step of evidence-based practice. Use the evidence pyramid to help you to determine the best study types to answer your PICO clinical question.

Levels of Evidence

Studies can be categorized and assigned a level based on the strength of the evidence and methodology. The levels of evidence can be visualized as a pyramid, with the strongest and most reliable evidence at the top and weaker evidence at the bottom. The amount of available evidence increases as you move down the pyramid, but decreases in quality.

Different types of clinical questions are best answered by different study types.  You might not always find the highest level of evidence to answer your question. When this happens, work your way down to the next highest level of evidence.

Filtered Evidence

The top of the pyramid represents the strongest evidence. These studies evaluate and synthesize the evidence for you.

• Practice guidelines

  Recommendations about best practice. They explain how to diagnose and manage a medical condition based on the evidence presented in higher level subject research such as systematic reviews, meta-analyses or comprehensive original research studies.
• Meta-analyses

  A meta-analysis is a report combining multiple studies on the same question in order to validate and strengthen conclusions using statistical analysis.
• Systematic reviews

  A systematic review seeks to answer a specific research question by identifying, appraising and synthesizing previously published research.

To find filtered evidence, search databases for secondary source types.

Unfiltered Evidence

Further down the pyramid are studies that you will need to read, interpret and evaluate the application to practice.

• Randomized controlled trials

  A randomized controlled trial (RCT) is a clinical trial where participants are randomly assigned to either a treatment group or a control group. The test-treatment group receives the treatment being studied while the control group receives either an alternative treatment, no treatment, or a placebo. Effects of the treatments are monitored to determine the efficacy of the treatment while reducing bias in both researchers and participants.
• Cohort studies

  A cohort study is an observational study of groups selected by their exposure to factors hypothesized to influence occurrence of a particular disease or other outcome.
• Case control studies

  Case control studies are comparisons that start with the identification of persons with the disease or outcome of interest and a control (comparison, referent) group without the disease or outcome of interest. The relationship of an attribute is examined by comparing both groups with regard to the frequency or levels of outcome over time.
• Case series and case reports

  These are detailed reports of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient that usually describes an unusual or novel occurrence. Case reports are one of the cornerstones of medical progress and provide new ideas in medicine.
• Background information & expert opinion

  Information that can often be found in point-of-care resources, medical textbooks, handbooks, encyclopedias, and reference materials. Background information is important to consult when you need general information about a condition, medication, or diagnostic test. Expert opinion is a belief or interpretation by specialists with experience in a specific area.

To find unfiltered evidence, search databases for primary source types.

Questions & Help

If you have questions on this, or another, topic, contact a librarian for help!