title: Intraindividual variability in reaction time predicts cognitive outcomes 5 years later.
abstract: OBJECTIVE
  Building on results suggesting that intraindividual variability in reaction time (inconsistency) is highly sensitive to even subtle changes in cognitive ability, this study addressed the capacity of inconsistency to predict change in cognitive status (i.e., cognitive impairment, no dementia [CIND] classification) and attrition 5 years later.
  
  
  METHODS
  Two hundred twelve community-dwelling older adults, initially aged 64-92 years, remained in the study after 5 years. Inconsistency was calculated from baseline reaction time performance. Participants were assigned to groups on the basis of their fluctuations in CIND classification over time. Logistic and Cox regressions were used.
  
  
  RESULTS
  Baseline inconsistency significantly distinguished among those who remained or transitioned into CIND over the 5 years and those who were consistently intact (e.g., stable intact vs. stable CIND, Wald (1) = 7.91, p < .01, Exp(β) = 1.49). Average level of inconsistency over time was also predictive of study attrition, for example, Wald (1) = 11.31, p < .01, Exp(β) = 1.24.
  
  
  CONCLUSIONS
  For both outcomes, greater inconsistency was associated with a greater likelihood of being in a maladaptive group 5 years later. Variability based on moderately cognitively challenging tasks appeared to be particularly sensitive to longitudinal changes in cognitive ability. Mean rate of responding was a comparable predictor of change in most instances, but individuals were at greater relative risk of being in a maladaptive outcome group if they were more inconsistent rather than if they were slower in responding. Implications for the potential utility of intraindividual variability in reaction time as an early marker of cognitive decline are discussed.
authors.affiliation: Ageing Research Unit, Centre for Mental Health Research, Building 63, Eggleston Road, Australian National University, Canberra ACT 0200, Australia. allison.bielak@anu.edu.au
authors.forename: Allison A M
authors.initials: AA
authors.lastname: Bielak
authors.forename: David F
authors.initials: DF
authors.lastname: Hultsch
authors.forename: Esther
authors.initials: E
authors.lastname: Strauss
authors.forename: Stuart W S
authors.initials: SW
authors.lastname: Macdonald
authors.forename: Michael A
authors.initials: MA
authors.lastname: Hunter
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001288:Attention / Q000502:physiology; D002755:Choice Behavior; D003071:Cognition / Q000502:physiology*; D003072:Cognition Disorders / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D006801:Humans; D007206:Individuality; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009483:Neuropsychological Tests; D011237:Predictive Value of Tests; D011930:Reaction Time / Q000502:physiology*; D012044:Regression Analysis; D012111:Residence Characteristics; D016019:Survival Analysis