GRADE DESCRIPTION I Evidence obtained from at least one properly randomized controlled trial. II-1 Evidence obtained from well-designed controlled trials without randomization. II-2 Evidence obtained from well-designed cohort or case-control analytic studies, preferably from more than one center or research group. II-3 Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled experiments (such as the results of the introduction of penicillin in the 1940s) could also be regarded as this type of evidence. III Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees. M Supported by at least one meta-analysis. CE Supported by at least one cost-effectiveness or decision analysis study. *Based on the evidence grading system adopted by the US Preventive Services Task Force, as well as the system presented by Greengold & Weingarten in Developing Evidence Based Practice Guidelines And Pathways: The Experience At The Local Hospital Level¹. Journal On Quality Improvement 22:391-402, 1996.