Epworth sleepiness scale in obstructive sleep disordered breathing: the reliability and validity of the Thai version

The objectives of this study are to test the reliability and validity of the Thai version of the Epworth sleepiness scale (ESS) and to assess the relationship between the ESS score and the severity of obstructive sleep disordered breathing. A total of 228 subjects (149 males and 79 females) were recruited. In order to check the discriminant validity of the ESS, we included 32 healthy volunteers and 39 patients with primary snoring to be the control groups and 126 patients with obstructive sleep apnea (OSA) confirmed by full polysomnography to be the disease groups. The test-retest reliability was investigated in 71 subjects. To check the responsiveness properties of the questionnaire, we asked a separate group of 31 patients who were successfully treated with either continuous positive airway pressure (CPAP) or upper airway surgery to complete the ESS before and after treatment at 3-6 months. The internal consistency demonstrated by Cronbach's alpha coefficients for standardized item was 0.87 and a range from 0.84 to 0.86 if some items were deleted. The test-retest reliability was shown by intra-class correlation coefficients of 0.79. There was a statistically significant difference between the mean of the ESS scores of the control groups (6.1 +/- 3.0) and the OSA patients (9.9 +/- 5.3) (p < 0.001). The ESS scores decreased significantly after a successful treatment with both CPAP and surgery (p < 0.001); however, there was no statistically significant difference among different severities of OSA. Our Thai version of the ESS showed an excellent internal consistency and test-retest reliability. It is able to discriminate between control subjects and OSA patients and to assess the response of treatment; however, it has a weak relationship with the apnea-hypopnea index. Therefore, we recommend use it to combine with more comprehensive clinical evaluation in obstructive sleep disordered breathing patients.