The development and use of a new scale, the Epworth sleepiness scale (ESS), is described. This is a simple, self-administered questionnaire which is shown to provide a measurement of the subject's general level of daytime sleepiness. One hundred and eighty adults answered the ESS, including 30 normal men and women as controls and 150 patients with a range of sleep disorders. They rated the chances that they would doze off or fall asleep when in eight different situations commonly encountered in daily life. Total ESS scores significantly distinguished normal subjects from patients in various diagnostic groups including obstructive sleep apnea syndrome, narcolepsy and idiopathic hypersomnia. ESS scores were significantly correlated with sleep latency measured during the multiple sleep latency test and during overnight polysomnography. In patients with obstructive sleep apnea syndrome ESS scores were significantly correlated with the respiratory disturbance index and the minimum SaO2 recorded overnight. ESS scores of patients who simply snored did not differ from controls.

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SUMMARY Excessive daytime sleepiness (EDS) is an important symptom that needs to be quantified, but there is confusion over the best way to do this. Three of the most commonly used tests: the multiple sleep latency test (MSLT), the maintenance of wakefulness test (MWT) and the Epworth sleepiness scale (ESS) give results that are significantly correlated in a statistical sense, but are not closely related. The purpose of this investigation was to help clarify this problem. Previously published data from several investigations were used to calculate the reference range of normal values for each test, defined by the mean±2 SD or by the 2.5 and 97.5 percentiles. The 'rule of thumb' that many people rely on to interpret MSLT results is shown here to be misleading. Previously published results from each test were also available for narcoleptic patients who were drug-free at the time and who by definition had EDS. This enabled the sensitivity and specificity of the three tests to be compared for the first time, in their ability to distinguish the EDS of narcolepsy from the daytime sleepiness of normal subjects. The receiver operator characteristic curves clearly showed that the ESS is the most discriminating test, the MWT is next best and the MSLT the least discriminating test of daytime sleepiness. The MSLT can no longer be considered the gold standard for such tests.

Excessive daytime sleepiness in the general community is a newly recognized problem about which there is little standardized information. Our aim was to measure the levels of daytime sleepiness and the prevalence of excessive daytime sleepiness in a sample of Australian workers and to relate that to their self-reported sleep habits at night and to their age, sex, and obesity. Sixty-five percent of all 507 employees working during the day for a branch of an Australian corporation answered a sleep questionnaire and the Epworth sleepiness scale (ESS) anonymously. Normal sleepers, without any evidence of a sleep disorder, had ESS scores between 0 and 10, with a mean of 4.6 +/- 2.8 (standard deviation). They were clearly separated from the "sleepy" patients suffering from narcolepsy or idiopathic hypersomnia whose ESS scores were in the range 12-24, as described previously. ESS scores > 10 were taken to represent excessive daytime sleepiness, the prevalence of which was 10.9%. This was not related significantly to age (22-59 years), sex, obesity, or the use of hypnotic drugs but was related significantly but weakly to sleep-disordered breathing (frequency of snoring and apneas), the presence of insomnia, and reduced time spent in bed (insufficient sleep).