Development and Validation of the Incapacity Status Scale—Revised: a Novel, Multi-Dimensional Patient-Reported Measure of Disability in Multiple Sclerosis.
Portnoy, Jeffrey Glenn
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Multiple sclerosis (MS) is associated with a wide variety of symptoms affecting patients’ functioning and quality of life. Because of the heterogeneous clinical profile, existing methods of assessing disability and incapacity in MS suffer from limitations in psychometric validity, practicality of administration, and comprehensive representation of the MS illness experience. The most common primary outcome used in MS research, and subsequent scales based on it, rely on an outdated understanding of MS-related disability that overemphasizes ambulatory functioning at the expense of other impactful symptoms. Specifically, studies have shown that invisible elements of the disease profile have serious consequences for patients’ well-being and ability to function. This study developed a new patient-reported instrument, the Incapacity Status Scale—Revised (ISS-R), which aimed to better reflect the complex, multi-dimensional aspects of MS disability. The ISS-R is available in both computerized and pen-and-paper formats and can be completed in approximately five minutes. It assesses 16 areas of functioning, using adaptive questioning with precise anchoring statements to minimize subjectivity. Principal component analysis of the ISS-R yielded a two-component solution, corresponding to Physical and Mental/Sensory functions, prompting the creation of two subscales. Item and scale analyses demonstrated strong reliability, consistency, and discrimination for the total scale and subscales. The ISS-R showed strong convergent validity with a performance-based composite (r = −.547, p < .001) and with an array of domain-specific objective and self-reported physical and neuropsychiatric outcomes, reflecting the ISS-R’s ability to capably represent both visible and invisible elements of MS disability. Discriminant validity was strong. Subscales and items similarly demonstrated excellent construct validity. Scores from the ISS-R were used to create predictive models using receiver operating characteristic (ROC) curves for employment status (AUC = .819, p < .001), fall risk (AUC = .805, p < .001), depressive (AUC = .845, p < .001) and anxiety disorders (AUC = .749, p < .001), and cognitive impairment (AUC = .736, p < .001), supporting criterion validity and generating practical interpretive cutoff scores. The ISS-R is a promising new patient-reported outcome allowing clinicians and researchers to assess the multi-dimensional aspects of disability in MS.
Doctoral Dissertation, Ph.D., Ferkauf -- Open Access.
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