Evidence Based Practice Toolkit

Understanding types of resources

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

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