Physician Associate Studies: EBP: Levels of Evidence

Evidence-Based Practice: Study Design.
Medical Center Library and Archives, Duke University

Critically-appraised individual articles and synopses include:

Filtered evidence:

• Level I: Evidence from a systematic review of all relevant randomized controlled trials.
• Level II: Evidence from a meta-analysis of all relevant randomized controlled trials.
• Level III: Evidence from evidence summaries developed from systematic reviews
• Level IV: Evidence from guidelines developed from systematic reviews
• Level V: Evidence from meta-syntheses of a group of descriptive or qualitative studies
• Level VI: Evidence from evidence summaries of individual studies
• Level VII: Evidence from one properly designed randomized controlled trial

Unfiltered evidence:

• Level VIII: Evidence from nonrandomized controlled clinical trials, nonrandomized clinical trials, cohort studies, case series, case reports, and individual qualitative studies.
• Level IX: Evidence from opinion of authorities and/or reports of expert committee

Two things to remember:

1. Studies in which randomization occurs represent a higher level of evidence than those in which subject selection is not random.

2. Controlled studies carry a higher level of evidence than those in which control groups are not used.

• Example RCT
• Example Meta Analysis
• Example Case Control
• Example Case Series
• Example Cohort
• Example Cross-sectional