title: Does interval between screening and baseline matter in HD cognitive clinical trials?
abstract: BACKGROUND
  "Practice effects" (PE), or performance improvements due to prior exposure to testing, are known to confound cognitive test results, particularly when short intervals occur between two test sessions.
  
  
  OBJECTIVE
  We examined two subsamples with short or long re-test intervals from a recent clinical trial.
  
  
  METHODS
  Thirty-four non-depressed adults with mild Huntington Disease (HD) participated. Three cognitive tests were administered at screening and again at baseline, before active treatment randomization. Half the sample had a 24-hour retest interval while the other half was >6-days.
  
  
  RESULTS
  The two groups differed on demographic/clinical factors (age, Total Motor Score and Total Functional Capacity). After controlling for age and motor score, PE differences were found on three of the five UHDRS cognitive tests: the longer interval group showed larger PE on Symbol-Digit Modalities and Stroop color, while the rapid interval group had larger PE on Stroop interference. Controlling for screening cognitive performance yielded similar results.
  
  
  CONCLUSIONS
  Length of interval between screening and baseline visits and level of disease severity may influence stability of UHDRS cognitive test results in clinical trials in HD.
authors: University of Iowa, Iowa City, IA, USA Elks Rehab Hospital, Boise, ID, USA.
authors: Leigh J
authors: LJ
authors: Beglinger
authors: Loyola University Chicago, Chicago, IL, USA.
authors: William H
authors: WH
authors: Adams
authors: University of Iowa, Iowa City, IA, USA.
authors: Douglas
authors: D
authors: Langbehn
authors: University of Iowa, Iowa City, IA, USA.
authors: Jess G
authors: JG
authors: Fiedorowicz
authors: Mayo Clinic Scottsdale, Scottsdale, AZ, USA.
authors: John
authors: J
authors: Caviness
authors: University of Rochester, Rochester, NY, USA.
authors: Kevin
authors: K
authors: Biglan
authors: University of Iowa, Iowa City, IA, USA.
authors: Blair
authors: B
authors: Olson
authors: University of Iowa, Iowa City, IA, USA.
authors: Jane S
authors: JS
authors: Paulsen
mesh_terms: D000328:Adult; D003071:Cognition / Q000187:drug effects; D003072:Cognition Disorders / Q000175:diagnosis* / Q000209:etiology* / Q000523:psychology; D003704:Dementia / Q000175:diagnosis* / Q000209:etiology* / Q000523:psychology; D018450:Disease Progression; D005260:Female; D006801:Humans; D006816:Huntington Disease / Q000150:complications* / Q000188:drug therapy* / Q000523:psychology; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D012720:Severity of Illness Index; D013997:Time Factors
keywords: Huntington disease; cognitive disorders/dementia; neuropsychological assessment; practice effects