To determine the variability in annual Mini-Mental State Examination scores of patients with Alzheimer disease enrolled in the Consortium to Establish a Registry for Alzheimer's Disease (CERAD).

A total of 372 patients with probable Alzheimer disease with 1 or more years of follow-up.

Twenty-one CERAD clinical sites throughout the United States.

An average annual decline of 3.4 points in CERAD patients returning for longitudinal reassessments was close to the SD of the measurement error of 2.8 points for the Mini-Mental State Examination. There was wide variability in individual rates of decline. Even with 4 years of follow-up, 15.8% of the patients had no clinically meaningful decline in Mini-Mental State Examination score (defined as a change in initial score >3, ie, 1 SD of measurement error). Validity of measurements of the rate of change in Mini-Mental State Examination scores …