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NRS 302 - Nursing Research

Library instruction for Spring B 2022.

What is Evidence?

So, what is evidence anyway? Evidence is the scientific literature (or studies) published in peer-reviewed journals. In evidence based-practice, clinical evidence is used to inform patient care to reach ideal outcomes.

You will need to understand the types of studies and the research processes they follow. Different types of studies have different strengths depending on the clinical question you are trying to answer.

You will also need to use your search strategy in an appropriate database. See some suggestions below.

Levels of Evidence

Rating System for the Hierarchy of Evidence/Levels of Evidence

Level I
Evidence for a systematic review or meta-analysis of all relevant randomized controlled trials (RCTs) or evidence-based clinical practice guidelines based on systematic reviews of RCTs.

Level II
Evidence obtained from at least one well-designed randomized controlled trial.

Level III

Evidence obtained from one well-designed controlled trials without randomization.

Level IV
Evidence from well-designed case-control and cohort studies.

Level V
Evidence from systematic reviews of descriptive or qualitative study.

Level VI
Evidence from single descriptive or qualitative study.

Level VII

Evidence from the opinion of authorities and/or reports of expert committees.

Table from Melnyk, Bernadette Mazurek and Ellen Fineout-Overholt. Evidence-based practice in nursing and healthcare. Philadelphia : Lippincott Williams & Wilkins, 2005:10.

Primary and Secondary Sources

The pyramids of evidence break down source types that you will encounter while searching for evidence. Each source type is appropriate for answering different clinical questions.

Primary sources:

  • Building blocks of a body of literature.
  • Include published individual reports, studies, and trials.

Secondary sources

  • "Filtered" sources of information.
  • These gather, synthesize, evaluate, and summarize primary sources.
  • Higher quality because it has been further analyzed.

This pyramid breaks down and defines the different types of primary sources (with secondary sources at the top).

A Pyramid of Evidence” by New Literacies Alliance is licensed under CC BY-NC-SA 3.0.

This pyramid breaks down the different types of secondary sources.

Six S Pyramid

"6S Pyramid" by McMaster University Health Sciences Library is licensed under CC BY-NC-SA 4.0.

Nursing and Health Sciences Databases

If using a computer on the Aultman campus, choose the ON-SITE at NEOMED or any Associated Hospital link. Otherwise, choose the OFF-SITE link and log in. When prompted, select NEOMED or Northeast Ohio Medical University as your institution, enter your last name and your library ID.


Aultman Health Sciences Library


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