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Quantifying sleepiness

Neil Freedman, MD
Section Editor
Susan M Harding, MD, FCCP, AGAF
Deputy Editor
April F Eichler, MD, MPH


It is important to detect excessive sleepiness – defined as sleepiness that occurs in a situation when an individual would usually be expected to be awake and alert – because it is associated with morbidity and increased mortality, and can be treated in many cases [1]. However, self-reported sleepiness is generally subjective and imprecise, which has led to the development of tests to quantify an individual's sleepiness [2-5].

The multiple sleep latency test (MSLT) and the maintenance of wakefulness test (MWT) use objective measures to quantify sleepiness. The Oxford SLEep Resistance (OSLER) test, which is a simplified variation of the MWT, is another objective that can be used to indirectly quantify sleepiness. In contrast, the Epworth Sleepiness Scale (ESS) and Stanford Sleepiness Scale (SSS) subjectively quantify sleepiness.

Here, methods for quantifying sleepiness are described, and each of the tests used to quantify sleepiness is discussed. A general approach to the epidemiology, etiology, clinical features and evaluation of excessive daytime sleepiness is discussed separately. (See "Approach to the patient with excessive daytime sleepiness".)


The following definitions are important for understanding the discussion that follows:

Epoch – An epoch is a standard 30-second interval of a polysomnogram (PSG) to which a sleep stage is assigned. In special situations, an epoch can be longer or shorter.

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Literature review current through: Nov 2017. | This topic last updated: Feb 01, 2017.
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