Greater precision when measuring dementia severity: establishing item parameters for the Clinical Dementia Rating Scale.

BACKGROUND/AIMS An item response theory (IRT)-based scoring approach to the Clinical Dementia Rating Scale (CDR) can account for the pattern of scores across the CDR items (domains) and their differential abilities to indicate dementia severity. In doing so, an IRT-based approach can provide greater precision than other CDR scoring algorithms. However, neither a good set of item parameters nor an easily digestible set of instructions needed to implement this approach is readily available. METHODS Participants were 1,326 patients at the Baylor College of Medicine Alzheimer's Disease and Memory Disorders Clinic. RESULTS The item parameters necessary for an IRT-based scoring approach were identified (a parameters ranged from 3.01 to 6.22; b parameters ranged from -2.46 to 2.07). CONCLUSION This study provides, and demonstrates how to easily apply, IRT-based item parameters for the CDR