Overview
Not all studies are created equal. Use the following Levels of Evidence to help determine the strength of the articles you find so you can find the best evidence, not just the first results.
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