title: Reliability of the Alzheimer's disease assessment scale (ADAS-Cog) in longitudinal studies.
abstract: BACKGROUND
  Considering the scarcity of longitudinal assessments of reliability, there is need for a more precise understanding of cognitive decline in Alzheimer's Disease (AD). The primary goal was to assess longitudinal changes in inter-rater reliability, test retest reliability and internal consistency of scores of the ADAS-Cog.
  
  
  METHODS
  2,618 AD subjects were enrolled in seven randomized, double-blind, placebo-controlled, multicenter-trials from 1986 to 2009. Reliability, internal-consistency and cross-sectional analysis of ADAS-Cog and MMSE across seven visits were examined.
  
  
  RESULTS
  Intra-class correlation (ICC) for ADAS-Cog was moderate to high supporting their reliability. Absolute Agreement ICCs 0.392 (Visit-7) to 0.806 (Visit-2) showed a progressive decrease in correlations across time. Item analysis revealed a decrease in item correlations, with the lowest correlations for Visit 7 for Commands (ICC=0.148), Comprehension (ICC=0.092), Spoken Language (ICC=0.044).
  
  
  CONCLUSIONS
  Suitable assessment of AD treatments is maintained through accurate measurement of clinically significant outcomes. Targeted rater education ADAS-Cog items over-time can improve ability to administer and score the scale.
authors.affiliation: Nathan S. Kline Institute for Psychiatric Research, 1 Wards Island Complex, Wards Island New York, NY 10035, USA. akhan@nki.rfmh.org.
authors.forename: Anzalee
authors.initials: A
authors.lastname: Khan
authors.forename: Christian
authors.initials: C
authors.lastname: Yavorsky
authors.forename: Guillermo
authors.initials: G
authors.lastname: DiClemente
authors.forename: Mark
authors.initials: M
authors.lastname: Opler
authors.forename: Stacy
authors.initials: S
authors.lastname: Liechti
authors.forename: Brian
authors.initials: B
authors.lastname: Rothman
authors.forename: Sofija
authors.initials: S
authors.lastname: Jovic
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000175:diagnosis* / Q000523:psychology; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D012720:Severity of Illness Index