TABLE 3.

Classification of level of evidence for recommendations^*

Level of evidence	Definition
Level I	Based on randomized, controlled trials (or meta-analysis of such trials) of adequate size to ensure a low risk of incorporating false-positive or false-negative results
Level II	Based on randomized, controlled trials that are too small to provide Level I evidence. These may show either positive trends that are not statistically significant or no trends, and are associated with a high risk of false-negative results
Level III	Based on nonrandomized, controlled or cohort studies, case series, case controlled studies or cross-sectional studies
Level IV	Based on the opinion of respected authorities or that of expert committees as indicated in published consensus conferences or guidelines

^*This classification scheme has been previously used in Canadian Infectious Disease Society Position Papers (133)