The primary analyses involved a comparison of pregabalin and placebo over a period of 12 weeks with use of the International RLS ( IRLS ) Study Group Rating Scale ( on which the score ranges from 0 to 40 , with a higher score indicating more severe symptoms ) , the Clinical Global Impression of Improvement scale ( which was used to assess the proportion of patients with symptoms that were `` very much improved '' or `` much improved '' ) , and a comparison of rates of augmentation with pregabalin and pramipexole over a period of 40 or 52 weeks of treatment .