title: Cross-sectional versus longitudinal estimates of cognitive change in nondemented older people: a CERAD study. Consortium to Establish a Registry for Alzheimer's Disease.
abstract: OBJECTIVE
  To investigate the effect of increasing age on cognition in nondemented older people.
  
  
  METHODS
  A cross-sectional and longitudinal analysis.
  
  
  METHODS
  A total of 454 control subjects for Alzheimer's cases from the cohort assembled by the Consortium to Establish a Registry for Alzheimer's Disease (CERAD).
  
  
  METHODS
  The Mini-Mental State Examination (MMSE) to assess cognitive function.
  
  
  RESULTS
  Cross-sectional estimates were derived by generalized linear models and longitudinal estimates by generalized estimating equations. The cross-sectional model indicated a small but significant decline in MMSE of -.4 points per 10 years. The longitudinal model indicated a small but significant increase in MMSE of about +.6 points per 10 years. Evidence of an early learning effect and nonrandom dropout exists.
  
  
  CONCLUSIONS
  The question of "normal" aging can be approached by considering cross-sectional information and, usually separately, longitudinal information. This study does both using recently developed statistical methods. We conclude that there is a small but significant decline in scores on the MMSE with increasing population age. The effect can be masked in longitudinal cohorts by a learning effect (especially early in follow-up) and other factors associated with repeated testing.
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000544:Alzheimer Disease / Q000453:epidemiology; D003071:Cognition; D003072:Cognition Disorders / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008609:Mental Status Schedule; D008875:Middle Aged