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Types of Evidence
Meta-Analysis A systematic review that uses quantitative methods to summarize the results.
Systematic Review An article in which the authors have systematically searched for, appraised, and summarized all of the medical literature for a specific topic.
Critically Appraised Topic Authors of critically-appraised topics evaluate and synthesize multiple research studies.
Critically Appraised Articles Authors of critically-appraised individual articles evaluate and synopsize individual research studies.
Randomized Controlled Trials RCT's include a randomized group of patients in an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.
Cohort Study Identifies two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
Case-Control Study Involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking to see if they had the exposure of interest.
Background Information / Expert Opinion Handbooks, encyclopedias, and textbooks often provide a good foundation or introduction and often include generalized information about a condition. While background information presents a convenient summary, often it takes about three years for this type of literature to be published.
Animal Research / Lab Studies Information begins at the bottom of the pyramid: this is where ideas and laboratory research takes place. Ideas turn into therapies and diagnostic tools, which then are tested with lab models and
Levels of Evidence
Rating System for the Hierarchy of Evidence: Quantitative Questions
Level I: Evidence from a systematic review of all relevant randomized controlled trials (RCT's), or evidence-based clinical practice guidelines based on systematic reviews of RCT's
Level II: Evidence obtained from at least one well-designed Randomized Controlled Trial (RCT)
Level III: Evidence obtained from well-designed controlled trials without randomization, quasi-experimental
Level IV: Evidence from well-designed case-control and cohort studies
Level V: Evidence from systematic reviews of descriptive and qualitative studies
Level VI: Evidence from a single descriptive or qualitative study
Level VII: Evidence from the opinion of authorities and/or reports of expert committees
Melnyk, B., & Fineout-Overholt, E. (2011). Evidence-based practice in nursing & healthcare: A guide to best practice (2nd ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, p. 10.