title: Cohort effects in age-associated cognitive trajectories.
abstract: BACKGROUND
  The age-specific prevalence and incidence of dementia and cognitive impairment in the United States have either remained stable or even slightly declined during the 1980s-1990s. A suggested but untested reason for this improvement in cognitive function over time is higher educational attainment among more recent cohorts.
  
  
  METHODS
  We used data from two large prospective population-based epidemiological dementia studies conducted in two adjacent regions during the period 1987-2012. We examined whether (i) cohort effects could be observed in age-associated trajectories of cognitive functions and (ii) the observed cohort effects could be explained by educational attainment. Trajectories of neuropsychological tests tapping three domains (psychomotor speed, executive function, and language) were compared among cohorts born between 1902 and 1911, 1912 and 1921, 1922 and 1931, and 1932 and 1943. We examined Age × Cohort interactions in mixed-effects models with/without controlling for education effects.
  
  
  RESULTS
  Cohort effects in age-associated trajectories were observed in all three domains, with consistent differences between the earliest born cohort and the most recent cohort. Executive functions showed the strongest and persistent differences between the most recent and other three cohorts. Education did not attenuate any of these associations.
  
  
  CONCLUSIONS
  Cohort effects were observed in all examined cognitive domains and, surprisingly, remained significant after controlling for educational effects. Factors other than education are likely responsible for the cohort effects in cognitive decline.
authors.affiliation: Department of Neurology, Oregon Health & Science University, Portland. Department of Neurology and hdodge@med.umich.edu dodgeh@ohsu.edu.
authors.forename: Hiroko H
authors.initials: HH
authors.lastname: Dodge
authors.affiliation: Department of Biostatistics, University of Michigan, Ann Arbor.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Biostatistics.
authors.forename: Ching-Wen
authors.initials: CW
authors.lastname: Lee
authors.affiliation: Department of Biostatistics, Department of Medicine, and.
authors.forename: Chung-Chou Ho
authors.initials: CC
authors.lastname: Chang
authors.affiliation: Department of Epidemiology, University of Pittsburgh, Pennsylvania. Department of Psychiatry, University of Pittsburgh School of Medicine, Pennsylvania.
authors.forename: Mary
authors.initials: M
authors.lastname: Ganguli
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000523:psychology*; D003071:Cognition / Q000502:physiology*; D003072:Cognition Disorders / Q000453:epidemiology / Q000523:psychology*; D056344:Executive Function / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D009483:Neuropsychological Tests; D010414:Pennsylvania / Q000453:epidemiology; D015995:Prevalence; D011446:Prospective Studies
keywords: Cognitive aging; Cognitive impairment; Dementia; Epidemiology; Socioeconomic status.