“…However, of those studies, only nine of 21 (43%) explicitly reported blinding of patients, clinicians, and/or assessors to the participants' treatment arm allocation [4,12,15,20,24,27,29,47,48]. Only nine of 21 (43%) reported performing an a priori power calculation for the outcome of postoperative cognitive dysfunction [4,16,24,27,29,34,38,39,48], with one of these studies failing to recruit a sufficient number of patients [38]. Of the remaining seven studies, two used a prospective comparative design [2,41], two used a case-control design [33,44], and three used a retrospective comparative design [17,19,36].…”