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Reliability and validity studies of the Turkish version of the Epworth Sleepiness Scale

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The Epworth Sleepiness Scale (ESS) is a self-administered eight-item questionnaire that is widely used in English speaking countries for assessment of daytime sleepiness in adults. The aim of this study was to investigate the reliability and validity of the ESS in the Turkish language. The Turkish version of the ESS (ESStr) was applied to 194 healthy controls and 150 consecutive subjects attending the sleep centre with symptoms of sleep-disordered breathing. Test–retest reliability of the ESStr was tested in a separate group of 30 subjects. The ESStr scores of 60 subjects with mild to severe obstructive sleep apnoea (OSA) were compared with the ESStr scores of 60 healthy controls matched for age, gender, and body mass index (BMI). Concurrent validity with the Functional Outcomes of Sleep Questionnaire (FOSQtr) was also assessed in 12 subjects. The questionnaire had a high level of internal consistency as measured by Cronbach’s alpha (≥0.86). The test–retest intraclass correlation coefficient was r  = 0.81 (95% confidence interval: 0.64–0.90) (p < 0.001) and Spearman’s correlation coefficient was r = 0.80 (p = 0.01). The control group had lower ESStr scores than subjects with sleep-disordered breathing (3.6 ± 3 vs 12.6 ± 6, respectively; p < 0.001). Subjects with mild sleep-disordered breathing also had lower scores of the ESStr than those with moderate and severe sleep-disordered breathing (10 ± 6.2 vs 14 ± 5. and 10 ± 6.2 vs 16 ± 5.4, respectively; both p < 0.05), but there were no significant differences between moderate and severe subjects with sleep apnoea. There were significant correlations between the ESStr and total FOSQtr and its subscales (r  = −0.22 to r = −0.92; all p  = 0.05). Factor analysis of item scores showed that the ESStr had only one factor. The ESStr is a reliable and valid measure of daytime sleepiness. These features and the simplicity of the ESStr make it a valuable measure for clinical management and research.

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Thank you very much to all the subjects who gave their time for this study. Thanks are also due to Dr. Jon Balserak for reviewing the text to ensure that the level of English is good.

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Correspondence to Bilgay Izci.


Appendix A: The Epworth Sleepiness Scale

How likely are you to doze off or fall asleep in the following situations, in contrast to feeling just tired? This refers to your usual way of life in recent times. Even if you have not done some of these things recently, try to work out how they would have affected you. Use the following scale to choose the most appropriate number for each situation.


  • 0 = would never doze

  • 1 = slight chance of dozing

  • 2 = moderate chance of dozing

  • 3 = high chance of dozing


Chance of dozing (enter number below)

Sitting reading


Watching TV


Sitting, inactive in a public place (e.g. a theatre or a meeting)


As a passenger in a car for an hour without a break


Lying down to rest in the afternoon when circumstances permit


Sitting and talking to someone


Sitting quietly after lunch without alcohol


In a car, when stopped for a few minutes in the traffic

  1. TOTAL....................

Appendix B: Turkish version of Epworth Sleepiness Scale

Son zamanlarda, günlük yaşantınız içinde, aşağıda belirtilen durumlarda hangi sıklıkla uyuklarsınız (buradan yorgun hissetmek değil, uyuklamak veya uyuya kalmak anlaşılmalıdır)? Bu şeylerden birini son zamanlarda yapmamış olsanız bile, böyle bir durumun, sizi nasıl etkileyeceğini düşünmeye çalışarak cevap veriniz.

Ölçekteki herbir DURUM için, aşağıdaki ifadelere karşılık gelen sayılardan, sizin için en uygununu isaretleyiniz.

  • 0 = hiçbir zaman uyuklamam

  • 1 = nadiren uyuklarım

  • 2 = zaman zaman uyuklarım

  • 3 = büyük olasılıkla uyuklarım

Table 6

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Izci, B., Ardic, S., Firat, H. et al. Reliability and validity studies of the Turkish version of the Epworth Sleepiness Scale. Sleep Breath 12, 161–168 (2008).

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