Measuring the impact of multiple sclerosis: Enhancing the measurement performance of the Multiple Sclerosis Impact Scale (MSIS-29) using Rasch Measurement Theory (RMT)

Sophie Cleanthous, Stefan Cano, Elizabeth Kinter, Patrick Marquis, Jennifer Petrillo, Xiaojun You, Craig Wakeford, Guido Sabatella, Sophie Cleanthous, Stefan Cano, Elizabeth Kinter, Patrick Marquis, Jennifer Petrillo, Xiaojun You, Craig Wakeford, Guido Sabatella

Abstract

Background: Study objectives were to evaluate the Multiple Sclerosis Impact Scale (MSIS-29) and explore an optimized scoring structure based on empirical post-hoc analyses of data from the Phase III ADVANCE clinical trial.

Methods: ADVANCE MSIS-29 data from six time-points were analyzed in a sample of patients with relapsing-remitting multiple sclerosis (RRMS). Rasch Measurement Theory (RMT) analysis was undertaken to examine three broad areas: sample-to-scale targeting, measurement scale properties, and sample measurement validity. Interpretation of results led to an alternative MSIS-29 scoring structure, further evaluated alongside responsiveness of the original and revised scales at Week 48.

Results: RMT analysis provided mixed evidence for Physical and Psychological Impact scales that were sub-optimally targeted at the lower functioning end of the scales. Their conceptual basis could also stand to improve based on item fit results. The revised MSIS-29 rescored scales improved but did not resolve the measurement scale properties and targeting of the MSIS-29. In two out of three revised scales, responsiveness analysis indicated strengthened ability to detect change.

Conclusion: The revised MSIS-29 provides an initial evidence-based improved patient-reported outcome (PRO) instrument for evaluating the impact of MS. Revised scoring improves conceptual clarity and interpretation of scores by refining scale structure to include Symptoms, Psychological Impact, and General Limitations.

Clinical trial: ADVANCE (ClinicalTrials.gov identifier NCT00906399).

Keywords: MSIS-29; Multiple sclerosis; Rasch Measurement Theory; clinical trials; post-hoc analysis; psychometrics.

Figures

Figure 1.
Figure 1.
Multiple Sclerosis Impact Scale (MSIS-29) sample-to-scale targeting. The top pink histogram shows the distribution of Physical Impact (a) and Psychological Impact (b) in the sample, and the lower blue histogram shows the distribution of impact in the MSIS-29 scale item thresholds and mean item locations, which map out the 20 (a) and 9 (b) impact items.
Figure 1.
Figure 1.
Multiple Sclerosis Impact Scale (MSIS-29) sample-to-scale targeting. The top pink histogram shows the distribution of Physical Impact (a) and Psychological Impact (b) in the sample, and the lower blue histogram shows the distribution of impact in the MSIS-29 scale item thresholds and mean item locations, which map out the 20 (a) and 9 (b) impact items.
Figure 2.
Figure 2.
Exemplar item characteristic curve (ICC). The ICC plots the scores expected by the Rasch model for each individual item on the y-axis at each and every level of the measurement continuum of Physical Impact (x-axis). The black dots represent observed scores in each of the 10 class intervals of the trait (i.e. Physical Impact). This ICC for Item 9 indicates slight under-discrimination of the trait, as the line indicated by the dots is flatter than the expected curve. Individuals with higher impact (right hand-side of the continuum) scored lower than expected denoting lower impact, while patients with lower impact (left hand-side of the continuum) scored higher than expected denoting more impact.
Figure 3.
Figure 3.
Raw score to interval metric transformation. The x-axis represents the Physical Impact construct as an interval logit score with increasing impact from left to right and the y-axis the raw score as calculated by the summed total of the Multiple Sclerosis Impact Scale (MSIS–29).
Figure 4.
Figure 4.
Revised Multiple Sclerosis Impact Scale (MSIS-29) sample-to-scale targeting. The top pink histogram shows the distribution of General Symptoms (a), Psychological Impact (b) and General Limitation (c) in the sample and the lower blue histogram shows the distribution of impact in the MSIS-29 scale item thresholds and mean item locations, which map out the 14 (a), 5 (b) and 10 (c) items.
Figure 4.
Figure 4.
Revised Multiple Sclerosis Impact Scale (MSIS-29) sample-to-scale targeting. The top pink histogram shows the distribution of General Symptoms (a), Psychological Impact (b) and General Limitation (c) in the sample and the lower blue histogram shows the distribution of impact in the MSIS-29 scale item thresholds and mean item locations, which map out the 14 (a), 5 (b) and 10 (c) items.

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