Development and Psychometric Validation of the Testamentary Capacity Assessment Screening Tool: A Study of Older Adults With and Without Dementia

OBJECTIVE: To develop and validate the Testamentary Capacity Assessment Screening Tool (TCAST) for older adults, addressing the absence of standardised instruments for testamentary capacity (TC) assessment in Japan. METHODS: The TCAST was developed through an iterative process including literature review, interdisciplinary expert consultation, and user testing with older adults. It comprises three subtests: (1) Hypothetical will-making Scenario, (2) Basic financial concepts, and (3) Legal vocabulary. Internal consistency, test-retest reliability, and construct validity were examined using Cronbach's α, intraclass correlation coefficients (ICC), and correlations with the Hasegawa Dementia Scale-Revised (HDS-R), the Executive Interview (EXIT25), and the Geriatric Depression Scale (GDS-15). Group comparisons and receiver operating characteristic (ROC) analyses were conducted to evaluate discriminatory performance. RESULTS: A total of 118 participants-68 cognitively healthy older adults and 50 with dementia-completed the TCAST. Internal consistency was good for Parts 1 and 2 (α = 0.88, 0.70) and lower for Part 3 (α = 0.58). Test-retest reliability was excellent for Parts 1 and 2 (ICC = 0.87, 0.89) and moderate for Part 3 (ICC = 0.58). Construct validity was supported by moderate to strong correlations with HDS-R and EXIT25, but not with GDS-15. All subtests correlated negatively with age and positively with education, and significantly differentiated healthy and dementia groups (p < 0.001). ROC analyses showed strong discriminatory capacity (AUC = 0.86, 0.97, and 0.79 for Parts 1-3). CONCLUSIONS: The TCAST is a reliable and valid screening tool for assessing TC in older Japanese adults. It is not designed to categorically determine incapacity, but to highlight domains relevant to testamentary reasoning and support person-centered evaluations. The tool may aid clinicians and legal professionals in identifying both retained abilities and areas needing support, underscoring its potential utility in interdisciplinary approaches to capacity assessment in aging societies.