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Nursing Library Orientation: 1c. Evidence Levels of Peer-Reviewed Articles

An online library orientation for nursing students.

1c. Levels of Evidence in the Nursing Literature

Now that you know how to limit your results to peer-reviewed journals and how to identify peer-reviewed articles, it is time to learn about the different LEVELS OF EVIDENCE among peer-reviewed articles. Evidence-based nursing seeks to make decisions based on the best available evidence, and all research designs and methodologies are NOT created equal. Watch this brief video to learn about the evidence pyramid. 

University of Louisville Libraries. (2018, January 30). Levels of evidence [Video]. YouTube.

Below is one example of an evidence pyramid. Note that the higher on the pyramid you look, the higher the quality of the information, but the fewer articles there are of that type. 


Also take a look at the Johns Hopkins Evidence Level and Quality Guide for descriptions of the different levels of evidence. 

Image used with permission of University of Massachusetts Lamar Soutter Library. 

You might have noticed that there are quite a few different versions of evidence pyramids. Despite their differences, all of these pyramids distinguish between PRIMARY research (original, empirical studies) and SECONDARY research (appraised summaries of an article or selection of articles).


  • Primary research is also called UNFILTERED research. The highest level of primary evidence is RANDOMIZED CONTROL TRIALS.  


  • Secondary research is also called FILTERED research. The highest levels of secondary evidence are considered to be SYSTEMATIC REVIEWS, META-ANALYSES, and CLINICAL PRACTICE GUIDELINES.

CINAHL: Scroll down from the main search box and try these limiters (try one at a time!)

  •  Search by Publication Type: Select Clinical Guideline, Meta-Analysis, Randomized Control Trial or Systematic Review.  Hold down the “Ctrl” key to select more than one publication type.  

  •  Check off 'Evidence-Based Practice'  to find articles from evidence-based practice journals, articles about EBP, research articles, and commentaries on research articles.

  •  Check off 'Research Articles' (all types of research)

  • Note on restricting to NURSING JOURNALS: you can check off "first author is a nurse" or "any author is a nurse" or select "Nursing" from the Journal Subset. 


PUBMED: Limiters are available on the left-hand side of the search results page

  • Under "Article Type" You can check off Meta-Analysis, Randomized Control Trial, and/or Systematic Review 

  • Additional Filters: Under "Additional Filters" click "Journal" and then "Nursing Journals" to limit to nursing journals