Statistical issues in prevention and therapeutic trials of Alzheimer disease.

Relatively little attention has been given to the proper design and statistical analysis of prevention and therapeutic trials of Alzheimer disease (AD). A number of important methodological issues arise in studies of AD that do not typically arise in studies of other chronic diseases. These issues include: the definition of the primary study endpoint that is simple to measure and easy to interpret; proper design of trials that take into account that the patient population is very old; and the proper statistical analysis that addresses the high drop out rate and the multiple ways of measuring disease severity. Addressing these issues will speed the progress of the evaluation of promising compounds to prevent and treat AD.