The use of clinical experience to stage the severity of functional impairments in Alzheimer's disease

Experienced clinicians from Germany and the United States rated the stage of Alzheimer's disease at which each of 44 manifestations of cognitive, behavioural, or functional impairment is considered most clinically relevant. The resulting data were subjected to three methods of metric scale analysis with the dual objective of examining international consistency and elucidating internationally-based clinical understanding of the chronology of increasing functional impairment in Alzheimer's disease. Preliminary examination of the data resulted in elimination of 6 judges for inconsistent performance. The remaining 28, approximately equally divided between Germany and the US, provided acceptably consistent results that were the basis for establishing metric distances between the 44 impairment items based on a combination of equal appearing intervals, principal components, and paired comparison scaling methods. The resulting ordering and associated scale values for the 44 items provide a consistent description of the course of functional impairments in Alzheimer's disease as seen by experienced clinicians in the two countries.