German translation, cultural adaptation for Austria, and validation of the Neurological Sleep Index-Multiple Sclerosis

Study objectives: To translate, culturally adapt, and validate the Neurological Sleep Index-Multiple Sclerosis (NSI-MS) for use in Austrian German-speaking populations with multiple sclerosis.

Methods: Following established guidelines, the NSI-MS diurnal sleepiness, nonrestorative nocturnal sleep, and fragmented nocturnal sleep scales underwent forward-backward translation, with content and face validity, and cultural adaptation to Austria established. Construct validity was evaluated using Rasch analysis. Known-groups validity was examined, and comparisons were made with scales measuring multiple sclerosis fatigue, daytime sleepiness, sleep quality, anxiety, and depression. Reliability was assessed through Cronbach's alpha, Person Separation Index, Lin's concordance correlation coefficient, measurement error, and floor and ceiling effects. Data were merged with a historic English dataset for comparison between English and German language versions.

Results: The translation and cultural adaptation of the NSI-MS-German version were successful. Pretesting involved 30 populations with multiple sclerosis, while the validation included 400 populations with multiple sclerosis with mild-to-severe disability. The diurnal sleepiness, nonrestorative nocturnal sleep, and fragmented nocturnal sleep scales exhibited good fit parameters, were unidimensional, and invariant. NSI-MS-German version scales demonstrated excellent convergent and known-groups validity, internal consistency, person separation reliability, test-retest reliability, adequate measurement error, and low floor and ceiling effects. Pooling English and German datasets revealed that person estimates for the nonrestorative nocturnal sleep and fragmented nocturnal sleep scales are equivalent across versions, unlike the diurnal sleepiness scale.

Conclusions: The NSI-MS-German version demonstrates validity, reliability, and responsiveness in assessing diurnal sleepiness, nonrestorative nocturnal sleep, and fragmented nocturnal sleep in populations with multiple sclerosis, generating interval-level data, and shows equivalence between its English and German versions.

Clinical trial registration: Registry: German Clinical Trials Register (DRKS); Name: German translation, cultural adaptation for Austria and validation of the Neurological Sleep Index - Multiple Sclerosis (NSI-MS); URL: https://drks.de/search/en/trial/DRKS00025573; Identifier: DRKS00025573.

Citation: Seebacher B, Mildner S, Monschein T, et al. German translation, cultural adaptation for Austria, and validation of the Neurological Sleep Index-Multiple Sclerosis. J Clin Sleep Med. 2024;20(12):1923-1935.