Evidence Pyramid
“Evidence Pyramid” by Tufts University can be reused under the BY-NC-SA license 4.0
Ideal Study for Type of Question
You might not always find the highest level of evidence based on the pyramid (i.e., Evidence-based Clinical Practice Guidelines) to answer your question. When this happens, work your way down the evidence pyramid to the next highest level of evidence (i.e. Meta-analysis and systematic review).
Depending on the clinical question, different types of research studies will provide the best evidence. This table suggests study designs best suited to answer each type of clinical question.
Note: Clinical Practice Guidelines, meta-analysis, and systematic reviews often provide the best answers to clinical questions.
|
Type of Question |
Ideal Type of Study |
|
Therapy / Prevention |
Randomized controlled trial (RCT) > Cohort Study > Case Control |
|
Diagnosis |
Cohort Study > Case Control |
|
Prognosis |
Cohort Study > Case Control > Case Series / Case Report |
|
Etiology/Harm |
RCT > Cohort Study > Case Control |
|
Cost Analysis |
Economic Analysis |
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.