Abstract
OBJECTIVE: This study investigated whether the discrepancy between desired time in bed and desired total sleep time (DBST) index could be a meaningful indicator for assessing insomnia severity in a clinical sample of patients with insomnia. Furthermore, we sought to identify the mediators of the association between DBST and insomnia severity in individuals with insomnia. METHODS: We collected the medical records of 127 patients with insomnia. Each participant's DBST index was calculated using sleep indices, including time and duration variables. Psychological symptoms were investigated using the Insomnia Severity Index (ISI), Patients Health Questionnaire-9 items (PHQ-9), Generalized Anxiety Disorder-7, Dysfunctional Beliefs and Attitudes about Sleep-16 items (DBAS-16), and Epworth Sleepiness Scale. RESULTS: The DBST index was significantly correlated with the ISI (r=0.20, p<0.05), desired total sleep time (r=-0.52, p<0.001), and desired time in bed (r=0.32, p<0.01). Linear regression analysis revealed that insomnia severity was associated with age (β=-0.18, p=0.018), DBST (β=0.23, p=0.003), PHQ-9 (β=0.23, p=0.031), and DBAS-16 (β=0.42, p<0.001). The DBST directly influenced insomnia severity, although indirect effects of mediators were not significant. CONCLUSION: The DBST index directly influenced insomnia severity regardless of the mediating effects of psychological factors among a clinical sample of patients with insomnia. This finding implies that the DBST index can be a simple measure of insomnia severity, even among patients with insomnia.