Rationale for use of the Clinical Dementia Rating Sum of Boxes as a primary outcome measure for Alzheimer's disease clinical trials

BACKGROUND: We used the database of the Alzheimer's Disease Neuroimaging Initiative (ADNI) to explore the psychometric properties of the Clinical Dementia Rating Sum of Boxes (CDR-SB) to consider its utility as an outcome measure for clinical trials in early and mild, as well as later, stages of Alzheimer's disease (AD). METHODS: We assessed internal consistency, structural validity, convergent validity, and 2-year internal and external responsiveness of the CDR-SB using data from 382 subjects with early or mild AD at entry into the ADNI study. RESULTS: The CDR-SB assesses both cognitive and functional domains of AD disability. Mean scores declined nearly linearly; CDR-SB cognitive and functional subsums contributed equally to total scores at both very mild (early) and mild stages of the disease. CONCLUSIONS: The CDR-SB has psychometric properties that make it attractive as a primary outcome measure that comprehensively assesses both cognitive and functional disability in AD patients. It may prove particularly useful for studies in early, predementia stages of AD.