Registered Nurses' Association of Ontario

Levels of Evidence



Evidence obtained from meta-analysis or systematic reviews of randomized controlled trials.


Evidence obtained from at least one randomized controlled trial.


Evidence obtained from at least one well-designed controlled study without randomization.


Evidence obtained from at least one other type of well-designed quasi-experimental study, without randomization.


Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, correlation studies and case studies.


Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities.

Adapted from “Annex B: Key to evidence statements and grades of recommendations,” by the Scottish Intercollegiate Guidelines Network (SIGN), 2012, in SIGN 50: A Guideline Developer’s Handbook. Available from



Clinical Management
Assessment and Management of Pain - 3rd Edition
Practice Recommendations