Rasch-based scoring offered more precision in differentiating patient groups in measuring upper limb function

Objective: To compare the discriminatory ability of Rasch-based and summative scoring in the context of assessing upper limb function of patients with stroke. Study Design and Setting: Data were from a cohort study of 497 adults with stroke undergoing physiotherapy. Upper limb function was assessed at admission and discharge using the upper limb subscale of the Motor Assessment Scale (UL-MAS). Rasch analysis was used to transform raw UL-MAS scores into interval measures. A relative precision (RP) index was used to differentiate patients by discharge destination. Results: The analysis confirmed the unidimensional structure of UL-MAS at both admission and discharge and demonstrated the adequate fit of the items. The RP index favored the Rasch-based scoring over the summative scoring in differentiating between the two patient groups, with significant gains in precision at admission (15%) and discharge (11%). When examining patients in the upper or lower quartile of UL-MAS, the gains in precision were statistically significant in favor of the Rasch-based scoring, with 20% precision at admission and 19% precision at discharge. Conclusion: Rasch-based scoring was more precise in differentiating patient groups by discharge destination than the summative scoring used to measure upper limb function, especially at the extreme range of the scale.