Table 2.

Quality of evidence

LEVEL	QUALITY OF EVIDENCE
I	There is evidence from at least 1 properly conducted randomized controlled trial
II	There is evidence from at least 1 well designed clinical trial without randomization, from cohort or case-control analytic studies (preferably from more than 1 centre), from multiple time-series studies, or from dramatic results in uncontrolled experiments
III	The evidence is from opinions of respected authorities based on clinical experience, descriptive studies, or reports of expert committees