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 |
|
Etiology |
Randomized controlled trial (RCT), meta-analysis, cohort study |
|
Diagnosis |
Randomized controlled trial (RCT) |
|
Prevention |
Randomized controlled trial (RCT), meta-analysis |
|
Prognosis |
Cohort study |
|
Meaning |
Qualitative study |
|
Quality Improvement |
Randomized controlled trial (RCT) |
|
Cost |
Economic evaluation |