title: Estimating premorbid cognitive abilities in low-educated populations.
abstract: OBJECTIVE
  To develop an informant-based instrument that would provide a valid estimate of premorbid cognitive abilities in low-educated populations.
  
  
  METHODS
  A questionnaire was drafted by focusing on the premorbid period with a 10-year time frame. The initial pool of items was submitted to classical test theory and a factorial analysis. The resulting instrument, named the Premorbid Cognitive Abilities Scale (PCAS), is composed of questions addressing educational attainment, major lifetime occupation, reading abilities, reading habits, writing abilities, calculation abilities, use of widely available technology, and the ability to search for specific information. The validation sample was composed of 132 older Brazilian adults from the following three demographically matched groups: normal cognitive aging (n = 72), mild cognitive impairment (n = 33), and mild dementia (n = 27). The scores of a reading test and a neuropsychological battery were adopted as construct criteria. Post-mortem inter-informant reliability was tested in a sub-study with two relatives from each deceased individual.
  
  
  RESULTS
  All items presented good discriminative power, with corrected item-total correlation varying from 0.35 to 0.74. The summed score of the instrument presented high correlation coefficients with global cognitive function (r = 0.73) and reading skills (r = 0.82). Cronbach's alpha was 0.90, showing optimal internal consistency without redundancy. The scores did not decrease across the progressive levels of cognitive impairment, suggesting that the goal of evaluating the premorbid state was achieved. The intraclass correlation coefficient was 0.96, indicating excellent inter-informant reliability.
  
  
  CONCLUSIONS
  The instrument developed in this study has shown good properties and can be used as a valid estimate of premorbid cognitive abilities in low-educated populations. The applicability of the PCAS, both as an estimate of premorbid intelligence and cognitive reserve, is discussed.
authors.affiliation: Geriatrics Division, Department of Internal Medicine, University of São Paulo Medical School, São Paulo, São Paulo, Brazil. daniel.apolinario@usp.br
authors.forename: Daniel
authors.initials: D
authors.lastname: Apolinario
authors.forename: Sonia Maria Dozzi
authors.initials: SM
authors.lastname: Brucki
authors.forename: Renata Eloah de Lucena
authors.initials: RE
authors.lastname: Ferretti
authors.forename: José Marcelo
authors.initials: JM
authors.lastname: Farfel
authors.forename: Regina Miksian
authors.initials: RM
authors.lastname: Magaldi
authors.forename: Alexandre Leopold
authors.initials: AL
authors.lastname: Busse
authors.forename: Wilson
authors.initials: W
authors.lastname: Jacob-Filho
mesh_terms: D003072:Cognition Disorders / Q000503:physiopathology*; D004522:Educational Status; D005260:Female; D006801:Humans; D007360:Intelligence / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D025341:Principal Component Analysis; D011795:Surveys and Questionnaires
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