Nuisance parameters in the assessment of noncognitive manifestations of dementia.

Measures of noncognitive disturbances in dementia typically rely on ratings by informants. In this study, method variance in measures of affect, behavior, and functional competence was evaluated by comparing ratings from 2 types of informants (spouse vs. child) in patients with probable Alzheimer's disease. No differences were observed on 5 variables; for 2 measures of behavior disturbance and 1 measure of functional disability, ratings obtained from child informants were significantly higher than spouse ratings for patients at comparable levels of dementia severity. Although the effect of the rater dimension was relatively small and selective, the findings suggest the need for further research on potential sources of bias in the ratings of noncognitive features of the dementia syndrome.