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Table 1.

American Occupational Therapy Association Evidence-Based Literature Review Project Levels of Evidence Rating System

Level of Evidence Definitions 
Level I Systematic reviews, meta-analyses, randomized controlled trials 
Level II Two groups, nonrandomized studies (e.g., cohort, case-control) 
Level III One group, nonrandomized (e.g., before and after, pretest and posttest) 
Level IV Descriptive studies that include analysis of outcomes (e.g., single-subject design, case series) 
Level V Case reports and expert opinion that include narrative literature reviews and consensus statements 
Level of Evidence Definitions 
Level I Systematic reviews, meta-analyses, randomized controlled trials 
Level II Two groups, nonrandomized studies (e.g., cohort, case-control) 
Level III One group, nonrandomized (e.g., before and after, pretest and posttest) 
Level IV Descriptive studies that include analysis of outcomes (e.g., single-subject design, case series) 
Level V Case reports and expert opinion that include narrative literature reviews and consensus statements 

Note. From “Evidence-Based Medicine: What It Is and What It Isn’t” by D. L. Sackett, W. M. Rosenberg, J. A. Muir Gray, R. B. Haynes, & W. S. Richardson, 1996, British Medical Journal, 312, pp. 71–72. Copyright © 1996 by the British Medical Association. Adapted with permission.

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