Research Hub: Evidence Based Practice Toolkit: Levels of Evidence

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Levels of Evidence Table

Levels of evidence (sometimes called hierarchy of evidence) are assigned to studies based on the methodological quality of their design, validity, and applicability to patient care. These decisions gives the "grade (or strength) of recommendation."

Level of evidence (LOE)	Description
Level I	Evidence from a systematic review or meta-analysis of all relevant RCTs (randomized controlled trial) or evidence-based clinical practice guidelines based on systematic reviews of RCTs or three or more RCTs of good quality that have similar results.
Level II	Evidence obtained from at least one well-designed RCT (e.g. large multi-site RCT).
Level III	Evidence obtained from well-designed controlled trials without randomization (i.e. quasi-experimental).
Level IV	Evidence from well-designed case-control or cohort studies.
Level V	Evidence from systematic reviews of descriptive and qualitative studies (meta-synthesis).
Level VI	Evidence from a single descriptive or qualitative study.
Level VII	Evidence from the opinion of authorities and/or reports of expert committees.

This level of effectiveness rating scheme is based on the following: Ackley, B. J., Swan, B. A., Ladwig, G., & Tucker, S. (2008). Evidence-based nursing care guidelines: Medical-surgical interventions. (p. 7). St. Louis, MO: Mosby Elsevier.

Different types of clinical questions are best answered by different types of research studies. You might not always find the highest level of evidence (i.e., systematic review or meta-analysis) to answer your question. When this happens, work your way down to the next highest level of evidence.

This table suggests study designs best suited to answer each type of clinical question.

Clinical Question	Suggested Research Design(s)
All Clinical Questions	Systematic review, meta-analysis
Therapy	Randomized controlled trial (RCT), meta-analysis Also: cohort study, case-control study, case series
Etiology	Randomized controlled trial (RCT), meta-analysis, cohort study Also: case-control study, case series
Diagnosis	Randomized controlled trial (RCT) Also: cohort study
Prevention	Randomized controlled trial (RCT), meta-analysis Also: prospective study, cohort study, case-control study, case series
Prognosis	Cohort study Also: case-control study, case series
Meaning	Qualitative study
Quality Improvement	Randomized controlled trial (RCT) Also: qualitative study
Cost	Economic evaluation

Evidence Pyramid (Levels of Evidence)

"Evidence Pyramid" is a product of Tufts University and is licensed under BY-NC-SA license 4.0

Tufts' "Evidence Pyramid" is based in part on the Oxford Centre for Evidence-Based Medicine: Levels of Evidence (2009)

Research Designs in the Hierarchy

Definitions

SAGE Research Methods: Foundations This link opens in a new window
Provides introductory overviews to major research methodologies, research ethics, and biographical sketches of researchers.

Encyclopedia of Nursing Research by Joyce J. Fitzpatrick
Call Number: eBook
ISBN: 9780826133045
Publication Date: 2017-07-01
Comprehensive and concise, entries provide the most relevant and current research perspectives and demonstrate the depth and breadth of nursing research today. This one-stop reference presents key terms and concepts and clarifies their application to practice. The fourth edition has been substantially updated to contain the latest research for nurse scientists, educators, and students in all clinical specialties.

Oxford Centre for Evidence Based Medicine Glossary