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Alzheimer`s & Dementia
Year: 2011 | Volume: 7 | Issue: 6 | Page No.: 602 - 610
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Suitability of the Clinical Dementia Rating-Sum of Boxes as a single primary endpoint for Alzheimers disease trials
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Nicola Coley,
Sandrine Andrieu,
Mark Jaros,
Michael Weiner,
Jesse Cedarbaum
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Bruno Vellas
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Abstract: Background
Clinical measures continue to be used as primary endpoints for disease-modifying trials for Alzheimers disease (AD). Currently, two co-primary endpoints must be specified, which measure cognitive and functional impairments. Generally, the Alzheimers Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) is one of the co-primary endpoints, but high variability in this measure results in large sample sizes. We evaluated the psychometric properties of the Clinical Dementia Rating-Sum of Boxes (CDR-SB) to assess its suitability as a single primary endpoint as an alternative to the traditional co-primary approach.
Methods
Internal consistency, structural and convergent validity, and 2-year internal and external responsiveness of the CDR-SB were assessed in 667 very mild to moderate (global Clinical Dementia Rating, 0.52) AD patients from the REAL.FR (Reseau sur la Maladie d'Alzheimer Francais) study.
Results
The CDR-SB showed good internal consistency (Cronbachs alpha = 0.88), and acceptable structural (separate cognitive and functional factors) and convergent validity. Variability in mean changes over time was low, leading to excellent internal responsiveness (effect size = 1.2; standardized response mean = 1.17 at 2 years) and smaller sample sizes as compared with the ADAS-Cog. External responsiveness was acceptable when compared with clinically meaningful changes on the Activities of Daily Living scale but only borderline acceptable when compared with the ADAS-Cog and Instrumental Activities of Daily Living. Levels of missing data and floor/ceiling effects were low.
Conclusions
The CDR-SB measures cognitive and functional impairment simultaneously, and has excellent 2-year internal responsiveness. This makes it a promising candidate as a sole primary endpoint for AD trials, although more work is required to determine the clinical relevance of CDR-SB changes, and its usefulness as an endpoint at other disease stages. |
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