Registered Nurses' Association of Ontario

Levels of Evidence

Ia Evidence obtained from meta-analysis or systematic review of randomized controlled trials.
Ib Evidence obtained from at least one randomized controlled trial.
IIa 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.


Addiction and Mental Health
Assessment and Care of Adults at Risk for Suicidal Ideation and Behaviour
Practice Recommendations