The DBST Index, the Discrepancy Between Desired Time in Bed and Desired Total Sleep Time: The Possible New Sleep Index Predicting Severity of Insomnia

Background and Objective We considered the concept of the DBST, the discrepancy between a patient’s desired time in bed (TIB) and desired total sleep time (TST). The DBST index can be used to easily assess a patient’s thoughts on their desired TST and dysfunctionally long TIB. This study aimed to explore whether the DBST index can predict the severity of insomnia.Methods A total of 374 members of the general population participated in this e-survey study. The participants answered questions regarding their bedtime, sleep onset time, wake-up time, desired TST, and desired TIB, and psychological symptoms were assessed using the Insomnia Severity Index (ISI), Patients Health Questionnaire–9 items (PHQ-9), Dysfunctional Beliefs and Attitudes about Sleep–16 items (DBAS-16), and Glasgow Sleep Effort Scale (GSES).Results The DBST index was significantly correlated with the ISI (r = 0.20, p < 0.01), PHQ-9 (r = 0.15, p < 0.01), GSES (r = 0.14, p < 0.01), DBAS-16 (r = 0.16, p < 0.01), desired TST (r = -0.62, p < 0.01), and desired TIB (r = 0.52, p < 0.01). Linear regression analysis showed that insomnia severity was predicted by persistent preoccupation with sleep (beta = 0.64, p < 0.001), dysfunctional beliefs about sleep (beta = 0.06, p < 0.001), depression (beta = 0.23, p < 0.001), and DBST (beta = 0.32, p = 0.035). The DBST directly influenced insomnia severity, and this association was shown to be mediated by dysfunctional beliefs and attitudes about sleep, preoccupation with sleep, and depression.Conclusions The DBST index could be a possible new sleep index due to its relationship with insomnia severity, depression, dysfunctional beliefs about sleep, and preoccupation with sleep. Further studies are needed to explore the consistency of the clinical sample.