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Dement Geriatr Cogn Disord. 2009;27(4):344-52. doi: 10.1159/000209212. Epub 2009 Mar 17.

Agreement in cognitive and clinical assessments in Alzheimer's disease.

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  • 1Departments of Neurology, Biostatistics, Bioinformatics and Biomathematics, and Psychiatry, Georgetown University School of Medicine, Washington, D.C. 20057, USA.



To estimate agreement among scores on three common assessments of cognitive function.


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.


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.


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.

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