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Erschienen in:
04.01.2018 | Original studies
A German version of the Insomnia Severity Index
Validation and identification of a cut-off to detect insomnia
Erschienen in: Somnologie | Ausgabe 1/2018
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Background
Insomnia is a prevalent disorder. There is a need for brief, easily manageable, and valid questionnaires to support practitioners in the clinical evaluation of insomnia.
Objective
This paper assesses the psychometric properties, the discriminatory power and the optimal clinical cut-off point of a German version of the Insomnia Severity Index (ISI) with both a sample of patients with primary insomnia as well as a non-clinical sample.
Methods
Two datasets were used (N = 700). The first dataset is from an initial screening for a sleep training program for patients with insomnia (n = 416). The second dataset consists of a general sample (n = 284). The internal consistency, the factor structure, the construct validity, the discriminatory power and the optimal clinical cut-off point were calculated.
Results
The internal consistency of the German ISI was good (α = 0.83) and test–retest reliability (n = 143) was satisfactory (r = 0.78). Significant correlations between the ISI and measures of sleep quality, depression and stress reactivity confirmed the expectations regarding construct validity. The discriminatory power was excellent and the optimal cut-off point was >10 (sensitivity: 91%, specificity: 83%).
Conclusion
The findings demonstrate that the German version of the ISI has good psychometric properties and can be recommended as a measurement tool to quantify symptom severity for both research and clinical practice.