Purpose: This study aimed to generate the health state classification system (HCS) of a condition-specific preference-based measure to capture the health-related quality of life (HRQoL) of patients with myasthenia gravis (MG) from the 15-item Myasthenia Gravis Quality of Life Scale (MG-QoL15r).
Materials and methods: An HCS was derived from the MG-QoL15r in a large sample of 1739 patients with MG based on psychometric analysis, including factor analysis, item response theory analysis, and discussions with experts. Reliability, construct and convergent validity, and item fit of the HCS were further assessed using another sample.
Results: The HCS has six dimensions: social activity, hobbies and fun activities, meeting family needs, work performance, mobility, and emotion, and it demonstrates good internal consistency reliability. The unidimensionality of the HCS was confirmed using confirmatory factor analysis. Satisfied convergent validity was supported by a significant association with the 12-item Short Form Survey (SF-12).
Conclusions: Based on a solid process of development and consultations with clinical professionals and patients, a valid MG-specific preference-based measure, MGQoL-6D, was developed. Further research will estimate the local preference weight to support the MG-related cost-utility analysis.IMPLICATION FOR REHABILITATIONA new condition-specific health state classification system (HCS) named Myasthenia gravis Quality of Life Scale (MGQoL-6D) is proposed.MGQoL-6D classifies MG health states as a combination of six dimensions with three response levels.The dimensions of the HCS are social activity, hobbies and fun activity, family needs, work performance, mobility, and emotion.The HCS and the upcoming value set of the MGQoL-6D could support the cost-effectiveness analysis of MG-related clinical and rehabilitated interventions.
Keywords: Patient-reported outcome measure; condition-specific instrument; myasthenia gravis; preference-based measure; quality of life.