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Nursing Resources : Levels of Evidence (I-VII)

Levels of Evidence

Rating System for the Hierarchy of Evidence: Quantitative Questions

Level I: Evidence from a systematic review of all relevant randomized controlled trials (RCT's), or evidence-based clinical practice guidelines based on systematic reviews of RCT's

Level II: Evidence obtained from at least one well-designed Randomized Controlled Trial (RCT)

Level III: Evidence obtained from well-designed controlled trials without randomization, quasi-experimental

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

Level V: Evidence from systematic reviews of descriptive and qualitative studies

Level VI: Evidence from a single descriptive or qualitative study

Level VII: Evidence from the opinion of authorities and/or reports of expert committees

Above information from "Evidence-based practice in nursing & healthcare: a guide to best practice" by Bernadette M. Melnyk and Ellen Fineout-Overholt. 2005, page 10.

Additional information can be found at:

Where to Find the Evidence?

Systematic research review
Where are they found? Cochrane Library, PubMed, Joanna Briggs Institute

Clinical practice guidelines
Where are they found? Many places! Don't get resources like MDConsult.

National Guideline Clearinghouse (NGC) or choose "guideline" or "Practice Guidelines" within the Publication Type limit in PubMed or CINAHL.

Current Practice Guidelines in Primary Care (AccessMedicine)
      This handy guide draws information from many sources of the latest guidelines for preventive services, screening methods, and treatment approaches commonly encountered in the outpatient setting.

ClinicalKey also has a number of Guidelines:!/browse/guidelines​

Original research articles
Where are they found? CINAHL, MEDLINE, Proquest Nursing & Allied Health, PsycINFO, PubMed

Steps In Analyzing A Research Article

When choosing sources it is important for you to evaluate each one to ensure that you have the best quality source for your project. Here are common categories and questions for you to consider:



· Does the first sentence contain a clear statement of the purpose of the article (without starting....The purpose of this article is to.....)

· Is the test population briefly described?

· Does it conclude with a statement of the experiment’s conclusions?



· Does it properly introduce the subject?

· Does it clearly state the purpose of what is to follow?

· Does it briefly state why this report is different from previous publications?



· Is the test population clearly stated? Is it appropriate for the experiment? Should it be larger? more


· Is the control population clearly stated? Are all variables controlled? Should it be larger? more


· Are methods clearly described or referenced so the experiment could be repeated?

· Are materials clearly described and when appropriate, manufacturers footnoted?

· Are all statements and descriptions concerning design of test and control populations and materials

and methods included in this section?



· Are results for all parts of the experimental design provided?

· Are they clearly presented with supporting statistical analyses and/or charts and graphs when


· Are results straightforwardly presented without a discussion of why they occurred?

· Are all statistical analyses appropriate for the situation and accurately performed?



· Are all results discussed?

· Are all conclusions based on sufficient data?

· Are appropriate previous studies integrated into the discussion section?

Northern Arizona University