The measurement structure of the Mayo-Portland Adaptability Inventory-4 (MPAI-4) in individuals with acquired brain injury: Evidence from Rasch analysis and classical test theory in a Japanese cohort

The Mayo-Portland Adaptability Inventory-4 (MPAI-4) is widely used to assess comprehensive outcomes following acquired brain injury (ABI). Although a Japanese version is available, its psychometric properties have not been evaluated. This study examined the measurement properties of the Japanese MPAI-4. A cross-sectional study was conducted with 163 participants receiving post-discharge rehabilitation between June 2024 and June 2025 at rehabilitation facilities in Japan. Rasch analyses examined reliability, unidimensionality, item fit, category functioning, targeting and differential item functioning. Classical Test Theory analyses assessed internal consistency and factor structure. The Japanese MPAI-4 demonstrated a Person Separation Index of 0.89 and high internal consistency (Cronbach's α = 0.91). Rasch analysis identified departures from model assumptions, including multidimensionality and disordered category thresholds. Exploratory factor analysis suggested a multifactorial structure, although it did not clearly align with the original three-domain model. These findings indicate that the Japanese MPAI-4 captures multiple aspects of post-ABI functioning, reflecting the complexity of outcomes in community rehabilitation. Although measurement issues should be considered when interpreting scores, the study provides initial psychometric evidence for the Japanese MPAI-4. These findings may support its clinical use for comprehensive assessment of post-ABI functioning in Japan, while contributing to the cross-cultural evidence base for the MPAI-4.