The article of record as published may be found at https://doi.org/10.1093/milmed/usz066Excessive daytime sleepiness affects an estimated 20% of the general population. While the prevalence of sleepiness in the military is largely unknown, it is well established that short sleep duration is endemic. The reasons for this include: the demanding nature of their duties, shift work and 24-hour duty periods, deployments and exigencies of military service as well as sleep disorders. The Epworth Sleepiness Scale (ESS) is the most widely used sleep questionnaire and provides a self-assessment of daytime sleepiness. To date the clinical utility of this questionnaire in differentiating sleep disorders in military patients with sleep disorders has never been evaluated. Materials and Methods: The primary aim of this manuscript was to assess if Epworth Sleepiness Scale (ESS) scores differed between military personnel with insomnia, obstructive sleep apnea (OSA), comorbid insomnia/obstructive sleep apnea (COMISA), and a group with neither insomnia nor obstructive sleep apnea (NISA). This study assessed the clinical utility of the ESS in differentiating sleep disorders amongst a sample (N = 488) of U.S. military personnel with insomnia (n = 92), OSA (n = 142), COMISA (n = 221), and a NISA group (n = 33) which served as the control population. Results: In the present sample, 68.4% of service members reported excessive daytime sleepiness (EDS) with an ESS > 10. ESS scores differed between military personnel with COMISA (13.5 ± 4.83) and those with OSA only (11.5 ± 4.08; p < 0.001) and the NISA group (9.46 ± 4.84; p < 0.001). Also, ESS scores differed between patients with insomnia only (13.0 ± 4.84) and the NISA group (p < 0.01). Conclusions: Overall, the ESS had poor ability to differentiate sleep disorders. In military personnel, the ESS appears elevated in the most common sleep disorders, likely due to their insufficient sleep, and does not help to differentiate OSA from insomnia. Further studies are required to validate this questionnaire and determine an appropriate threshold value for abnormal sleepiness in the military population
