Investigating emergent symptomatology as an outcome measure in a behavioral study of Alzheimer's disease.

These retrospective analyses represent a pilot study of a potential new outcome, expected emergence. The Behavior Rating Scale for Dementia (BRSD) was administered at the baseline and 12-month visits of a multicenter study. The authors computed the rates at which each BRSD symptom emerged over 12 months in normal elderly control subjects (n=64). These normal rates were then applied as the expected emergent rate (EER) to a population of individuals with Alzheimer's disease (n=235). The comparison of expected emergence to observed emergence in Alzheimer's disease showed interpretable differences. EER assesses whether treatments limit emergence in the target, relative to the standard, population. The ratio of expected to observed emergence provides an intuitively appealing quantification of treatment efficacy and can be used with any instrument that uses categorical or frequency ratings.