Improving single-subject change assessment: deriving the minimal detectable change of questionnaires' ordinal scores from Rasch analysis measures.

PURPOSE: The minimal detectable change (MDC) of questionnaire ordinal scores (MDCord) is the smallest score difference exceeding the measurement error. Being ordinal, it suffers from flaws, successfully addressed by the Rasch analysis (RA) and its robust interval measures. However, RA measures struggle to become established, likely because scores are more straightforward. This study aims to derive the MDCord of two upper limb measures, the Fugl-Meyer Assessment-Upper Limb (FMA-UL) and the Functional Assessment Test for Upper Limb (FAST-UL), from the MDC of their RA interval measures (MDCint).

METHODS

Two methodologies are applied. The first, based on a sensitivity and specificity analysis, defines the MDCord as the score difference with the highest accuracy in identifying a change per the MDCint. The second derives the MDCord from RA strata, another MDCint formulation. Various computations are tested, possibly resulting in slightly different MDCord.

RESULTS

The MDCord of the FMA-UL from sensitivity and specificity analysis was 8 and 4-5 for the FAST-UL. Using RA strata, the FMA-UL MDCord was 8-10, and that of the FAST-UL was 4-5.

CONCLUSIONS

An easy-to-use MDCord has been provided for the FMA-UL and the FAST-UL, which, anchored to the RA MDCint, benefits from its robust measurement properties.

CLINICAL TRIALS REGISTRY: NA.