title: Practice effects due to serial cognitive assessment: Implications for preclinical Alzheimer's disease randomized controlled trials.
abstract: BACKGROUND
  Practice effects are characteristic of nearly all standard cognitive tasks when repeated during serial assessments and are frequently important confounders in clinical trials.
  
  
  METHODS
  We summarize evidence that gains in neuropsychological test performance scores associated with practice effects occur as artifactual changes associated with serial testing within clinical trials. We identify and emphasize such gains in older, non-cognitively impaired individuals and estimate an effect size of 0.25 for composite cognitive measures in older populations assessed three times in a 6- to 12-month period.
  
  
  RESULTS
  We identified three complementary approaches that can be used to attenuate practice effects: (1) massed practice in a prebaseline period to reduce task familiarity effects; (2) tests designed to reduce practice-related gains so that item-specific driven improvements are minimized by using tasks that minimize strategy and/or maximize interitem interference; and (3) well-matched alternate forms.
  
  
  CONCLUSIONS
  We have drawn attention to and increased awareness of practice effect-related gains that could result in type 1 or type 2 errors in trials. Successfully managing practice effects will eliminate a large source of error and reduce the likelihood of misinterpretation of clinical trials outcomes.
authors.affiliation: Litwin Zucker Center for the Study of Alzheimer's Disease, Feinstein Institute, Hofstra North Shore LIJ School of Medicine, Manhasset, NY, USA.
authors.forename: Terry E
authors.initials: TE
authors.lastname: Goldberg
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL, USA; Research Service, Miami VA Healthcare System, Miami, FL, USA.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Harvey
authors.affiliation: Wesnes Cognition, Streatley on Thames, UK.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Wesnes
authors.affiliation: Department of Neurology, Alpert Medical School of Brown University & Rhode Island Hospital, Providence, RI, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Snyder
authors.affiliation: Departments of Psychiatry, Neurology, and Gerontology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
authors.forename: Lon S
authors.initials: LS
authors.lastname: Schneider
keywords: Alzheimer's disease; Clinical trials; Cognition; Neuropsychology; Practice effects; Preclinical Alzheimer's disease; Serial assessment