title: Two-year progression from mild cognitive impairment to dementia: to what extent do different definitions agree?
abstract: OBJECTIVE
  To determine the 2-year outcome from 16 different current classifications of mild cognitive impairment (MCI) in a population-based sample.
  
  
  METHODS
  Prospective cohort study: baseline and 2-year follow-up phases.
  
  
  METHODS
  Large-scale multicenter study, United Kingdom.
  
  
  METHODS
  : Thirteen thousand four individuals aged 65 and older from the Medical Research Council Cognitive Function and Ageing Study. From this, a subsample of 2,640 individuals was selected and completed a more-detailed cognitive assessment. Individuals who underwent further assessment were asked to complete annual or 2-year follow-ups.
  
  
  METHODS
  Information on sociodemographic status, general health, cognitive impairment and functional ability were collected using a structured interview. Individuals were classified according to 16 different definitions of MCI. These were applied retrospectively.
  
  
  RESULTS
  The dominant outcome across definitions was an impairment that was not classifiable or reversion to normality. Progression to dementia was variable and generally poor. Overall progression was highest in classifications in which impairment extended to memory and nonmemory domains. Predictability was age dependent in some but not all classifications.
  
  
  CONCLUSIONS
  Current classifications of MCI have variable outcomes in population-based samples. Progression to dementia is relatively rare and is dependent on age and definition. Selection criteria developed for the clinic are based on a "high risk" approach that leads to exclusion of a large percentage of the impaired population who are neither normal nor demented and for whom no intervention options are currently available. A refined definition of this construct is urgently needed if MCI is to be used to predict dementia in population-based studies.
authors.affiliation: Medical Resarch Council Biostatistics Unit, Institute of Public Health, Cambridge, United Kindom.
authors.forename: Fiona E
authors.initials: FE
authors.lastname: Matthews
authors.forename: Blossom C M
authors.initials: BC
authors.lastname: Stephan
authors.forename: Ian G
authors.initials: IG
authors.lastname: McKeith
authors.forename: John
authors.initials: J
authors.lastname: Bond
authors.forename: Carol
authors.initials: C
authors.lastname: Brayne
mesh_terms: D000203:Activities of Daily Living / Q000145:classification; D000368:Aged; D000544:Alzheimer Disease / Q000145:classification / Q000175:diagnosis* / Q000453:epidemiology; D003072:Cognition Disorders / Q000145:classification / Q000175:diagnosis* / Q000453:epidemiology; D015331:Cohort Studies; D004185:Disability Evaluation; D018450:Disease Progression; D004739:England; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008403:Mass Screening; D008569:Memory Disorders / Q000145:classification / Q000175:diagnosis / Q000453:epidemiology; D008609:Mental Status Schedule / Q000706:statistics & numerical data; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D011446:Prospective Studies; D011594:Psychometrics