A More Efficient Outcome for Alzheimer Disease Research: the Item Response Theory Based Score for the Clinical Dementia Rating (CDR®)

CDR sum of boxes (CDR‐SB) is widely used as a primary outcome in Alzheimer disease (AD) research due to its reliability and accuracy. However, it is an ordinal rank measure instead of a continuous measure and therefore may not be able to capture subtle changes in cognition. Additionally, it weights each domain equally, without accounting for the patterns of the responses scores across CDR items. To generate a more optimal score, we developed a bi‐factor model based on the item response theory (IRT) which can account for different response pattern, item difficulty and discrimination level to provide an improved estimate of the dementia severity. We demonstrated the superiority of the IRT score in two independent cohorts.