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NURSING 412: Adult Health II

Levels of Evidence

How strong is the evidence found in your study? The following 'evidence pyramid' shows the strongest evidence (at the top) and the weakest evidence (at the bottom). In your paper you may discuss the relative strength of the evidence found in your different studies.

Adapted from Stillwell, Fineout-Overhold, Melynk, & Williamson (2010).

Qualitative Research

This evidence pyramid shows the relative evidence strength for different types of qualitative research.

Best Types of Studies for Clinical Queries

What is the best type of study for your question? Use this guide:

Levels of evidence

Where can you find the different types of studies? This is a list of appropriate databases where you can search for studies.


Level 1: Systematic Reviews & Meta-analysis of RCTs; Evidence-based Clinical Practice Guidelines

Search: Cochrane Database of Systematic Reviews | PubMed | MedlineCINAHL | Nursing Reference Center 

Level 2: One or more Randomized Control Trials (RCTs)

Search: PubMed | Medline | CINAHL

Level 3: Controlled Trials (no randomization)

Search: PubMed | Medline | CINAHL

Level 4: Case-control or Cohort study

Search: PubMed | Medline | CINAHL

Level 5: Systematic Review of Descriptive and Qualitative studies

Search: PubMed | Medline | CINAHL

Level 6: Single Descriptive or Qualitative Study

Search: PubMed | Medline | CINAHL

Level 7: Expert Opinion

Search:  Nursing Reference Center | PubMed | Medline | CINAHL

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