Research Guides: Evidence-Based Dentistry (EBD): Levels of Evidence

Evidence Pyramid

“Evidence Pyramid” by Tufts University can be reused under the BY-NC-SA license 4.0

Study Designs for Types of Research Questions

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

Table from Winona State University Darrell W. Krueger Library's Evidence Based Practice Toolkit.

Levels of Evidence Table

Knowing the levels of evidence will help you identify the strongest level of evidence and select the best articles available to answer your research questions. When conducting a search, look for the highest level of evidence first.

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.

Table from Winona State University Darrell W. Krueger Library's Evidence Based Practice Toolkit.