Evidence-Based Research:

Levels of Evidence Pyramid

One way to organize the different types of evidence involved in evidence-based practice research is the levels of evidence pyramid. The pyramid includes a variety of evidence types and levels.

• Filtered resources: pre-evaluated in some way
  • systematic reviews
  • critically-appraised topics
  • critically-appraised individual articles
• Unfiltered resources: typically original research and first-person accounts
  • randomized controlled trials
  • cohort studies
  • case-controlled studies, case series, and case reports
• Background information, expert opinion

The levels of evidence pyramid provides a way to visualize both the quality of evidence and the amount of evidence available. For example, systematic reviews are at the top of the pyramid, meaning they are both the highest level of evidence and the least common. As you go down the pyramid, the amount of evidence will increase as the quality of the evidence decreases.

Text alternative for Levels of Evidence Pyramid diagram

Filtered resources appraise the quality of studies and often make recommendations for practice. The main types of filtered resources in evidence-based practice are:

• systematic reviews
• critically-appraised topics
• critically-appraised individual articles

Scroll down the page to the Systematic reviews, Critically-appraised topics, and Critically-appraised individual articles sections for links to resources where you can find each of these types of filtered information.

Authors of a systematic review ask a specific clinical question, perform a comprehensive literature review, eliminate the poorly done studies, and attempt to make practice recommendations based on the well-done studies. Systematic reviews include only experimental, or quantitative, studies, and often include only randomized controlled trials.

You can find systematic reviews in these filtered databases:

You can also find systematic reviews in this unfiltered database:

To learn more about finding systematic reviews, please see our guide:

Authors of critically-appraised topics evaluate and synthesize multiple research studies. Critically-appraised topics are like short systematic reviews focused on a particular topic.

You can find critically-appraised topics in these resources:

Authors of critically-appraised individual articles evaluate and synopsize individual research studies.

You can find critically-appraised individual articles in these resources:

To learn more about finding critically-appraised individual articles, please see our guide:

You may not always be able to find information on your topic in the filtered literature. When this happens, you'll need to search the primary or unfiltered literature. Keep in mind that with unfiltered resources, you take on the role of reviewing what you find to make sure it is valid and reliable.

Note: You can also find systematic reviews and other filtered resources in these unfiltered databases.

The Levels of Evidence Pyramid includes unfiltered study types in this order of evidence from higher to lower:

• randomized controlled trials
• cohort studies
• case-controlled studies, case series, and case reports

You can search for each of these types of evidence in the following databases:

Background information and expert opinions are not necessarily backed by research studies. They include point-of-care resources, textbooks, conference proceedings, etc.