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EBM Resources

Processing the Hierarchy of Evidence

Evidence-Based Medicine categorizes evidence based on how it has been processed and been packaged for use in clinical practice. They fall into the categories of Non-appraised Research, Critically Appraised Research, and Summaries/ Guidelines. The following content is based largely on  the 3rd edition of Users' guide to the medical literature: a manual for evidence-based clinical practice by Guyatt G, et. al, (2015).

  • Non-appraised Research. (Also known as primary evidence or unfiltered evidence). These are individual studies or observations which may take the form of RCTs, other controlled or cohort trials, case reports, or case series. Some of the largest indexers (databases) of such studies and reports are PubMed (this includes MEDLINE), Embase, CINAHL, and Web of Science. Other databases include PsycINFO and the literature search element of ClinicalKey. Google Scholar may also be considered a source of on non-appraised research but it is not carefully built like the aforementioned databases and may bring in crowded results from non-biomedical disciplines.
  • Critically Appraised Research. (Also known as secondary evidence or filtered evidence). These publications are the result of critical appraisal which is the process of "carefully and systematically assessing the outcome of scientific research (evidence) to judge its trustworthiness, value and relevance in a particular context" (CEBMa). To be even more precise, "critical appraisal looks at the way a study is conducted and examines factors such as internal validity, generalizability and relevance". Basically, pre-appraised research looks at the research that has already been done on a topic and combines and evaluates it for you.
    • Syntheses. These can be either systematic reviews or a meta-analyses. (1) Systematic Reviews: seek to answer a defined clinical questions by using a "predetermined search strategy with the goal of reducing bias by identifying, appraising, and synthesizing all relevant studies (of sound methodology) on a particular topic". (2) Meta-analyses: systematic reviews that "use statistical techniques to synthesize the data from several studies into a single quantitative estimate or summary effect size". Meta-anlyses can only be produced if there is a enough data on a topic to statistically pool together and draw conclusions
    • Synopses: these are one-page synopses will quickly and concisely convey what some of the most significant systematic reviews and meta-analyses have concluded. Instead of reading the systematic review or meta-analysis yourself, you can turn to synopses for a meaningful explanation of what the authors of these large undertakings ultimately found. Some EBM pyramids will also include synopses of studies which may be helpful when no systematic reviews or meta-analyses have been created yet.
  • Summaries and Guidelines: these are regularly updated online resources (often found scattered across specialty journals and organization websites) that "integrate the body of evidence on a topic and aim to provide recommendations for optimal management" (Guyatt, 2015). Examples include...
    • Clinical Practice Guidelines
    • Clinical Pathways
    • Point-of-Care Tools
    • Evidence Updates


  1. Guyatt G, Rennie D, Meade MO, Cook DJ. eds. (2015). Users' Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice, 3rd ed New York, NY: McGraw-Hill.
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