The reliability and validity of the Korean version of the Epworth sleepiness scale

The Epworth sleepiness scale (ESS) is widely used to measure the subject's average sleep propensity across those different situations in daily life, particularly in patients with sleep-disordered breathing. The purposes of this study were to test the hypothesis that the Korean version of the ESS (KESS) is valid and evaluate its usefulness.

We developed the KESS, which involved translating into Korean and then translating back into English to check its accuracy. A total of 273 participants (181 obstructive sleep apnea (OSA)-37 mild, 61 moderate, 83 severe, 32 simple snoring and 60 normal) were included in this study. All subjects completed the overnight polysomnograph and 53 of the total subjects were randomly selected for a retest with the questionnaire approximately 2∼4 weeks later. The associations between KESS and the degree of OSA were examined through ANCOVA, adjusted for age, sex and BMI.

The total score and each item's score of KESS in patients with OSA were significantly higher than subjects with normal controls (p < 0.01). As the severity of OSA increased, the KESS showed significantly increasing patterns (p for trend <0.01). The KESS in patient groups showed good internal consistency (Cronbach's α = 0.90) and test-retest reliability (r = 0.78 to 0.93).

The KESS is a reliable and valid tool for screening patients with daytime sleepiness in Korea.