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Levels of Evidence and Study Design: Levels of Evidence

Information on study design and levels of evidence to help you evaluate the medical, nursing and health care literature

Levels of Evidence

This is a general set of levels to aid in critically evaluating evidence. It was adapted from the model presented in the book, Evidence-Based Practice in Nursing and Healthcare: A Guide to Best Practice (Melnyk & Fineout-Overholt, 2019). Some specialties may have adopted a slightly different and/or smaller set of levels.


Level I

Evidence from a clinical practice guideline based on systematic reviews or meta-analyses of randomized controlled trials. Is this is not available, then evidence from a systematic review or meta-analysis of random controlled trials.

Level II

Evidence from randomized controlled studies with good design.

Level III

Evidence from controlled trials that have good design but are not randomized.

Level IV

Evidence from case-control and cohort studies with good design.

Level V

Evidence from systematic reviews of qualitative and descriptive studies.

Level VI

Evidence from qualitative and descriptive studies.

Level VII

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

Evidence Pyramid

The pyramid below is a hierarchy of evidence for quantitative studies. It shows the hierarchy of studies by study design; starting with secondary and reappraised studies, then primary studies, and finally reports and opinions, which have no study design. This pyramid is a simplified, amalgamation of information presented in the book chapter “Evidence-based decision making” (Forest et al., 2019) and book Evidence-Based Practice in Nursing and Healthcare: A Guide to Best Practice (Melnyk & Fineout-Overholt, 2019).


         Levels of evidence

Evidence Table for Nursing

Advocate Health - Midwest provides system-wide evidence based practice resources. The Nursing Hub* has an Evidence-Based Quality Improvement (EBQI) Evidence Table, within the Evidence-Based Practice (EBP) Resource. It also includes information on evidence type, and a literature synthesis table.

*The Nursing Hub requires access to the Advocate Health - Midwest SharePoint platform.


  • Forrest, J. L., Miller, S. A., Miller, G. W., Elangovan, S., & Newman, M. G. (2019). Evidence-based decision making. In M. G. Newman, H. H. Takei, P. R. Klokkevold, & F. A. Carranza (Eds.), Newman and Carranza's clinical periodontology (13th ed., pp. 1-9.e1). Elsevier.

  • Melnyk, B. M., & Fineout-Overholt, E. (2019). Evidence-based practice in nursing and healthcare: A guide to best practice (4th ed.). Wolters Kluwer.