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Levels of Evidence

NPTE Research & EBP

Systematic review primary studies are summarized, appraised, and statistically combined
Randomized Controlled Trial experimental study with random assignment with control group
Cohort study prospective study, group with condition followed for defined time, comparison made to group without condition
Homogeneity free of variations in the directions and degree of results between studies in SR
Case control study Restrospective, group with condition compared with group without condition to determine factors that may have played a role in the condition.
Case report only one individual studied in depth
Level 1a Level of Evidence SR with homogeneity of multiple RCTs, randomization, lg # of pts, multicenter, substantial agreement in size and direction of treatment effects
Level 1b Level of Evidence Individual RCT with narrow confidence level, treatment effects precisely defined
Level 1c All or none case series. In absence of RCT, overwhelming evidence of substantial tx effect
Level 2a SR with homogeneity of cohort studies
Level 2b Individual cohort study or low quality RCT (small N)
Level 3a SR with homogeneity of case-control studies
Level 3b Individual case control study
Level 4 Case series and poor quality cohort and case control studies, largely descriptive
Level 5 expert opinion, observations not made on pts
CPG - clinical practice guideline expert consensus, SR, meta analysis, assist practitioner for health care for specific clinical circumstances
Created by: Jenwithonen