Graduated compression stockings for the prevention of post operative venous thromboembolism.

volume 5, issue 2, page 1, 2001 Levels of Evidence All studies were categorised according to the strength of the evidence based on the following classification system. Level I Evidence obtained from a systematic review of all relevant randomised controlled trials. Level II Evidence obtained from at least one properly designed randomised controlled trial. Level III.1 Evidence obtained from well designed controlled trials without randomisation. Level III.2 Evidence obtained from well designed cohort or case control analytic studies preferably from more than one centre or research group. Level III.3 Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled experiments. Level IV Opinion of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees. Introduction