Assessing cognition in Alzheimer disease research.

Because cognitive impairment is the central, defining symptom of Alzheimer disease, cognitive assessments commonly are used as primary or secondary measures of outcome in Alzheimer disease research. The authors review the cognitive functions that decline in this neurodegenerative disease and summarize the necessary features of appropriate cognitive performance tests. The characteristics, strengths, and weaknesses of the major cognitive batteries employed as outcome measures in Alzheimer disease research are reviewed. Finally, the recent contributions to the development of cognitive measures by the Alzheimer's Disease Cooperative Study are presented briefly, followed by discussion of some critical issues for future test development.