The iADRS as an integrated measure of cognition and function: Psychometric evidence from recent clinical trials in early symptomatic Alzheimer's disease

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INTRODUCTION: Psychometric evaluation of the integrated Alzheimer's Disease Rating Scale (iADRS) was performed using data from three randomized clinical trials (RCTs). METHODS: Traditional measurement properties of the iADRS were assessed using classical test theory (CTT). Rasch Measurement Theory (RMT) analyses evaluated response properties of cognitive and functional items across the disease severity continuum. Crosswalks between iADRS, Clinical Dementia Rating - Sum of Boxes (CDR-SB), and Mini-Mental State Examination (MMSE) were developed to provide estimates of score equivalence. RESULTS: CTT results confirm good psychometric properties of the iADRS, including reliability (Cronbach's alpha 0.79-0.84), concurrent validity with CDR-SB (range: -0.64-0.70), and sensitivity to change. RMT findings demonstrate improved reliability of the integrated scale (person-separation index [PSI] = 0.92) compared to components and highlight concurrent and overlapping progression of cognitive and functional decline. DISCUSSION: The findings confirm the psychometric strength of the iADRS as a fit-for-purpose integrated endpoint for RCTs in early symptomatic Alzheimer's disease (AD). Crosswalk tables facilitate interpretation of clinical trial findings in clinical practice. HIGHLIGHTS: Findings confirm integrated Alzheimer's Disease Rating Scale (iADRS) total score reliability, validity, and sensitivity. Using the Rasch Measurement Theory (RMT), iADRS item set shows improved reliability relative to its component subscales. iADRS item thresholds are well distributed along the disease severity continuum. iADRS shows sensitivity to concurrent progression of cognitive and functional impairment. Crosswalk tables provide direct translation between iADRS, Clinical Dementia Rating - Sum of Boxes (CDR-SB), and Mini-Mental State Examination (MMSE).

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