Agreement in cognitive and clinical assessments in alzheimer's disease

Abstract

Aims: To estimate agreement among scores on three common assessments of cognitive function. Method: Baseline responses on the Alzheimer's Disease Assessment Scale - Cognitive, Clinical Dementia Rating, and the Mini-Mental State Examination were obtained from two clinical trials (n = 138 and n = 351). A graphical method of examining agreement, the means-difference or Bland-Altman plot, was followed by Levene's test of the equality of variance corrected for multiple comparison within each sample. Results: 70-78% of variability was shared by one factor, suggesting that all three instruments reflect cognitive impairment. However, agreement among tests was significantly worse for individuals with greater-than-average, relative to individuals with less-than-average, cognitive impairment. Conclusions: Worse agreement between tests, as a function of increasing cognitive impairment, implies that interpretation of these tests and selection of coprimary cognitive impairment outcomes may depend on impairment level. © 2009 S. Karger AG, Basel.