Validity and reliability of the Danish version of the Pittsburgh Sleep Quality Index

Aim: The Pittsburgh Sleep Quality Index is a widely used measure of sleep quality. The validity and reliability of the Danish version of the instrument has not yet been established. The aim of this study is to establish the internal consistency, test-retest reliability and convergent validity of the Danish version of the Pittsburgh Sleep Quality Index in adolescents. Methods: Data were collected from 719 students from 17 different upper secondary schools. The sample consisted of 55% women, and the mean age of the sample was 17.87 (2.52) years. Data was collected on two occasions approximately 6 weeks apart using online surveys. Apart from the Pittsburgh Sleep Quality Index, the students also completed the five-item World Health Organization Well-being Index and the 10-item Perceived Stress Scale. For internal consistency the Cronbach's alpha was calculated, for test-retest reliability the interclass correlation coefficient was computed, and for validity the Pearson's correlation was calculated. Results: The mean global Pittsburgh Sleep Quality Index score among Danish adolescents was 5.86 (3.13). The internal consistency for the Pittsburgh Sleep Quality Index was satisfactory with a Cronbach's alpha of 0.72. Test-retest reliability was adequate with an interclass correlation coefficient of 0.68. Finally, the Pittsburgh Sleep Quality Index showed large positive correlation with the 10-item Perceived Stress Scale (0.55) and a large negative correlation with the five-item World Health Organization Well-being Index (-0.59). Conclusions: The Danish version of the Pittsburgh Sleep Quality Index showed adequate reliability and validity among Danish adolescents.