Principal components analysis of agitation outcomes in Alzheimer's disease.

BACKGROUND:We developed a composite measure of agitation as a secondary outcome of change over time in the Citalopram for Agitation in Alzheimer's disease study (CitAD). CitAD demonstrated a positive effect of citalopram on agitation on the Neurobehavioral Rating Scale agitation subscale (NBRS-A). CitAD included additional agitation measures such as the Cohen-Mansfield Agitation Inventory and the Neuropsychiatric Inventory. METHODS:We performed principal components analyses on change in individual item of these scales for the same, original CitAD subjects. RESULTS:The first principal component accounted for 12.6% of the observed variance and was composed of items that appear to reflect agitation. The effect size for citalopram calculated using this component was 0.53 (95% CI 0.22-0.83) versus 0.32 for the NBRS-A (95% CI 0.01-0.62). CONCLUSIONS:Results suggest that a composite measure of change in agitation might be more sensitive than change in a single primary agitation measure.