The Epworth Sleepiness Scale quantifies the level of daytime sleepiness. The ratings to calculate the score are subjective and rely on the subject’s memory, which may be biased it the subject is trying to show he or she is sleepy or not sleepy.
The ESS was developed by Dr. Murray W. Johns at Epworth Hospital in Melbourne, Australia in the early 90s. The subjective test is intended to measure a person’s usual level of daytime sleepiness. The ESS asks the subject to rate his or her propensity to doze off in eight different situations. The various likelihoods are ranked from zero to three.
It presents the person with eight hypothetical situations: A score of 10 or more is considered sleepy. A score of 18 or more is very sleepy.
Use the following scale to choose the most appropriate number for each situation:
0 — no chance of nodding off
1 — slight chance of dozing
2 — moderate chance of sleeping
3 — high chance of falling asleep
Total score then runs from 0 to 24.
Based on experience with people known to have hypersomnia and other sleep disorders vs healthy people, the cutoff score of 10 has been established to identify excessive daytime sleepiness. Higher numbers mean the person is more sleepy. The ESS score has been found to correlate with the MSLT score, where an ESS score of 6 to 11 is intermediate on the MSLT scale, while a score of 12 and higher is high on the MSLT scale.
The ESS does not change over the course of a day (or several days) so is inappropriate for measuring changes in sleepiness. It is not a good tool for identifying acute sleepiness, either.
Advocates of the ESS claim it shows a person’s Average Sleep Propensity (ASP) which is different from fatigue or tiredness which is the focus of some other sleep scales (e.g. Stanford Sleepiness Scale). ASP is a measurement of a person’s general level of daytime sleepiness. The ESS should not be used to compare subjects to one another which limits its use as a research tool; however, a patient’s score may be used to compare the effects of treatment or stressors in that same patient over time.
In the late 1980s doctors at the University of Pittsburgh medical school devised an index to help diagnose and evaluate sleep quality. Dubbed the Pittsburgh Sleep Quality Index (PSQI) this self-rated questionnaire looks at sleep quality and disturbances over a one-month interval.
A recent study published in the journal Sleep showed that Epworth and PSQI scores tend to be stable when participants took the test over different times. The stability of the scores suggests that these scales have validity.