title: Propositional density and cognitive function in later life: findings from the Precursors Study.
abstract: OBJECTIVE
  We used longitudinal data from the Johns Hopkins Precursors Study to test the hypothesis that written propositional density measured early in life is lower for people who develop dementia categorized as Alzheimer's disease (AD). This association was reported in 1996 for the Nun Study, and the Precursors Study offered an unprecedented chance to reexamine it among respondents with different gender, education, and occupation profiles.
  
  
  METHODS
  Eighteen individuals classified as AD patients (average age at diagnosis: 74) were assigned 2 sex-and-age matched controls, and propositional density in medical school admission essays (average age at writing: 22) was assessed via Computerized Propositional Idea Density Rater 3 linguistic analysis software. Adjusted odds ratios (ORs) for the matched case-control study were calculated using conditional (fixed-effects) logistic regression.
  
  
  RESULTS
  Mean propositional density is lower for cases than for controls (4.70 vs. 4.99 propositions per 10 words, 1-sided p = .01). Higher propositional density substantially lowers the odds of AD (OR = 0.16, 95% confidence interval = 0.03-0.90, 1-sided p = .02).
  
  
  CONCLUSIONS
  Propositional density scores in writing samples from early adulthood appear to predict AD in later life for men as well as women. Studies of cognition across the life course might beneficially incorporate propositional density as a potential marker of cognitive reserve.
authors.affiliation: Department of Population, Family, and Reproductive Health, Johns Hopkins Bloomberg School of Pubic Health, 615 North Wolfe Street, Room E4647, Baltimore, MD 21205, USA. mengelma@jhsph.edu
authors.forename: Michal
authors.initials: M
authors.lastname: Engelman
authors.forename: Emily M
authors.initials: EM
authors.lastname: Agree
authors.forename: Lucy A
authors.initials: LA
authors.lastname: Meoni
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Klag
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000175:diagnosis / Q000523:psychology; D016022:Case-Control Studies; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D016001:Confidence Intervals; D004522:Educational Status; D005260:Female; D006801:Humans; D008037:Linguistics; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D016017:Odds Ratio; D011237:Predictive Value of Tests; D012307:Risk Factors; D012737:Sex Factors; D014956:Writing; D055815:Young Adult