Journals of Gerontology Series B: Psychological Sciences and Social Sciences, Vol 51, Issue 4 P217-P225, Copyright © 1996 by The Gerontological Society of America
The effects of preclinical dementia on estimates of normal cognitive functioning in aging
M Sliwinski, RB Lipton, H Buschke and W Stewart
Saul R. Korey Department of Neurology, Albert Einstein College of Medicine, USA. sliwinsk@aecom.yu.edu
Individuals with preclinical dementia have begun to decline cognitively,
but still perform within normal limits on cognitive testing. As a group,
subjects with preclinical dementia have lower scores on neuropsychological
tests than their dementia-free counterparts. This study examines the
effects of preclinical dementia on estimates of normal cognitive function
in the aged using data from a longitudinal study. Individuals with
preclinical dementia at baseline were retrospectively identified based on
subsequent development of dementia. Age-adjusted norms were computed using
baseline data for the Selective Reminding Test and the WAIS verbal and
performance scores, both including (conventional norms) and then excluding
(robust norms) preclinical cases. The results indicate that by failing to
exclude preclinical dementia, conventional normative studies underestimate
the mean, overestimate the variance, and overestimate the effect of age on
cognitive measures. Methods are discussed for selecting robust elderly
samples that are relatively free of contamination by preclinical dementia.
