Registered Nurses' Association of Ontario

Levels of Evidence

Levels of Evidence

Level Type 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.

III Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, correlation studies, and case  studies. 
IV Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. 

Evidence obtained from qualitative inquiry was included throughout this  guideline. Although recognized as important evidence that is “transformational” in its contribution to the  nurse’s understanding of best practice, universally accepted strategy comparable to  the  systems developed for  the  interpretation  of quantitative evidence do not  yet exist (Sandelowski, 2004).

Chronic Disease
Nursing Care of Dyspnea: The 6th Vital Sign in Individuals with Chronic Obstructive Pulmonary Disease (COPD)
Practice Recommendations