Registered Nurses' Association of Ontario

Levels of Evidence

The recommendations made in this best practice guideline have been critically reviewed and categorized by level of evidence. The following taxonomy provides the definitions of the levels of evidence and the rating system.


LEVEL Ia: Evidence obtained from meta-analysis of randomized controlled trials, plus consensus.

LEVEL Ib: Evidence obtained from at least one randomized controlled trial, plus consensus.

LEVEL II: Evidence obtained from at least one well-designed controlled study without randomization or evidence obtained from at least one other type of well-designed quasi-experimental study, plus consensus.

LEVEL III: Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, correlation studies and case studies, plus consensus.

LEVEL IV: Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities, plus consensus.

Clinical Management
Risk Assessment and Prevention of Pressure Ulcers
Practice Recommendations