Rate of cognitive change in Alzheimer's disease: Methodological approachesusing random effects models

Subtraction of serial scores, Least Squares Estimators, and Best Linear Unb iased Predictors (BLUPs) were compared for estimating rates of cognitive ch ange for Mini-Mental State Exam (MMSE) and Dementia Rating Scale (DRS) scor es for 299 probable Alzheimer's disease patients. The BLUPs provided cleane r group estimates of subjects' intercepts and slopes and are preferred. Reg ression analysis of the BLUP estimates of rate of change indicated that ste eper declines were associated with higher levels of education and older ace at onset. These effects were much smaller than those due to estimated init ial cognitive test score. Differences in longitudinal metric characteristic s of the MMSE and DRS were found, with the DRS yielding more precise change estimates. We discuss modeling these longitudinal data, and discuss use of the estimates of rate of change and intercept as data in their own right.