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Abstract Purpose The aim of this study was to validate the Ethos Brief Index (EBI) in patients with Restless Legs Syndrome (RLS). Methods A cross-sectional design, including 788 subjects with RLS (65% women, 70.8 years, SD 11.3) from the Swedish RLS Association, was used. A postal survey was sent out to collect data regarding socio demographics, comorbidities, and RLS-related treatment data. Questionnaires included were EBI, the Restless Legs Syndrome-6 Scale (RLS-6), Restless Legs Syndrome—Quality of Life questionnaire (RLSQoL), the Insomnia Severity Index (ISI), and the Epworth Sleepiness Scale (ESS). The validity and reliability of the EBI were investigated using Rasch and confirmatory factor analysis (CFA) models. Measurement invariance, unidimensionality, and differential item functioning (DIF) across age and gender groups, as well as insomnia, daytime sleepiness, RLS-related QoL and RLS severity were assessed. Results The results supported the unidimensionality of the EBI in the CFA (i.e., explaining 61.5% of the variance) and the Rasch model. The reliability of the EBI was confirmed using composite reliability and Cronbach’s alpha. No DIF was identified for gender, age, insomnia, daytime sleepiness, RLS severity or RLS-related QoL. Conclusion The EBI showed good validity and reliability and operated equivalently for male and female patients with RLS. Accordingly, healthcare professionals can use the EBI as a psychometrically sound tool to explore and identify patient-centered problems related to the whole life situation.
Knutsson et al. (Tue,) studied this question.