In this phase 3 , randomised , multicentre , double-dummy , placebo-controlled , 12-week , non-inferiority trial , adult patients with chronic stable plaque psoriasis ( for 12 months ) who were candidates for systemic or phototherapy and had a Psoriasis Area and Severity Index ( PASI ) score of 12 or higher and a Physician 's Global Assessment ( PGA ) of moderate or severe , and had failed to respond to , had a contraindication to , or were intolerant to at least one conventional systemic therapy , were enrolled from 122 investigational dermatology centres worldwide .