Chronic sleep reduction in adolescents—clinical cut-off scores for the Chronic Sleep Reduction Questionnaire (CSRQ) JULIA F. DEWALD-KAUFMANN 1,2,3 , EDUARD J. BRUIN 2 , MARCEL SMITS 4 , BONNE J.H. ZIJLSTRA 2 , FRANS J. OORT 2 and ANNE MARIE MEIJER 2 1 Hochschule Fresenius, University of Applied Sciences, Munich, Germany; 2 Research Institute of Child Development and Education, Faculty of Social and Behavioral Sciences, University of Amsterdam, Amsterdam, the Netherlands; 3 Department of Psychiatry and Psychotherapy, University Hospital LMU, Munich, Germany; 4 Centre for Sleep–Wake Disorders and Chronobiology, Hospital Gelderse Vallei, Ede, the Netherlands Keywords delayed sleep–wake phase disorder, insomnia, self-report, sleep debt, sleep problems Correspondence Julia F. Dewald-Kaufmann, Hochschule Fresenius, University of Applied Sciences, Munich, Germany Tel.: +4989200037324; fax: +4989200037330; e-mail: julia.dewald_kaufmann@med.uni- muenchen.de Accepted in revised form 27 November 2017; received 15 August 2017 DOI: 10.1111/jsr.12653 SUMMARY The Chronic Sleep Reduction Questionnaire is a validated questionnaire that measures symptoms of prolonged insufficient and/or poor sleep and therefore accounts for individuals’ sleep need and sleep debt. This study extends its psychometric properties by providing cut-off scores, using a matched sample of 298 healthy adolescents (15.38 Æ 1.63 years, 37.9% male, mean Chronic Sleep Reduction Questionnaire score: 32.98 Æ 6.51) and 298 adolescents with insomnia/delayed sleep–wake phase disorder (15.48 Æ 1.62 years; 37.9% male, mean Chronic Sleep Reduction Questionnaire score: 42.59 Æ 7.06). We found an area under the curve of 0.84 (95% confidence interval: 0.81–0.87). Cut-off scores for optimal sensitivity, optimal specificity and based on Youden’s criterion are provided. These cut-off scores are highly relevant for use of the Chronic Sleep Reduction Questionnaire in future studies and clinical practice. INTRODUCTION Although adolescents often suffer from insufficient and/or poor sleep (Gradisar et al., 2011), sleep variables such as sleep duration do not account for individuals’ sleep need and sleep debt. Sleep duration may therefore give an incomplete representation of adolescents’ sleep problems and its day- time consequences (e.g. Curcio et al., 2006; Dewald et al., 2010; Gregory and Sadeh, 2012). To overcome this problem, Meijer (2008) developed the Chronic Sleep Reduction Questionnaire (CSRQ), a subjective assessment tool that measures symptoms of chronic sleep reduction, rather than sleep directly. The questionnaire is based on the assumption that prolonged insufficient and/or poor sleep results in chronic sleep reduction, which causes impaired daytime functioning (Dewald-Kaufmann et al., 2013; Meijer, 2008). A high score on the CSRQ therefore indicates that adolescents have developed daytime impairments that are related to chroni- cally reduced sleep. The psychometric properties of a Dutch and an English version of the CSRQ have been evaluated and it was shown to be a reliable and valid measurement (Dewald et al., 2012), making it a promising indicator of chronic sleep reduction (Ji and Liu, 2016). Although a cross- sectional study demonstrated clear differences in daytime functioning between adolescents with low and high chronic sleep reduction (Dewald-Kaufmann et al., 2013), clinical cut- off scores have only been provided for a short version of the questionnaire, showing good discrimination abilities between clinical and healthy adolescents (Van Maanen et al., 2014). A clinical cut-off score of the CSRQ would, however, enhance its usefulness by allowing to screen for adolescents who suffer from clinically relevant reduced sleep, sleep debt and daytime impairments. Cut-off scores are important for the clinical practice (e.g. early detection of sleep problems to prevent the development of more severe sleep disorders and psychiatric diseases such as depression) and future research. The present study aims to calculate cut-off scores, using data from a large sample of adolescents with delayed sleep–wake phase disorder (DSWPD), insomnia and healthy controls. We included patients with insomnia and DSWPD as clinical groups, as they refer to the sleep disorders with high prevalence rates during adolescence (e.g. Johnson et al., 2006; Roberts et al., 2008; Saxvig et al., 2012). Furthermore, both groups are characterized by poor sleep quality and/or later sleep onset times which, in combination with early school start times in the morning, lead to impaired daytime ª 2018 European Sleep Research Society 1 of 4 J Sleep Res. (2018) 27, 1–4 Insomnia