Level I: Evidence from a systematic review or meta-analysis of all relevant RCTs
Level II: Evidence obtained from well-designed RCTs
Level III: Evidence obtained from well-designed controlled trials without randomization
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 single descriptive or qualitative studies
Level VII: Evidence from an opinion of authorities and/ or reports of expert committees
Further information: Evidence Based Practice Toolkit
More information about different study types: Literature Reviews: Types of Clinical Study Designs
» Glossary - Research Basics and Terminology
