How the Epworth Sleepiness Scale works
The Epworth Sleepiness Scale asks one question eight times over: in this particular situation, how likely are you to actually nod off? It deliberately avoids asking whether you feel tired, because tiredness and sleepiness are not the same thing. Someone recovering from flu feels wiped out but could not fall asleep in a meeting if they tried. Someone with fragmented sleep can feel perfectly alert at their desk and still lose consciousness the moment a train journey gets boring. The scale is built to catch the second kind of person.
The eight situations differ in how easy it is to fall asleep in them. Because they span that range, the total tells you roughly how far your sleep pressure reaches. Dozing only in the most restful situations is ordinary. Dozing in situations that demand attention is not.
Murray Johns published the scale in 1991 at the Epworth Hospital in Melbourne, comparing healthy adults with patients who had diagnosed sleep disorders, and followed it a year later with a reliability and factor analysis showing that the eight items hold together as a single measure. It has stayed essentially unchanged since, which is unusual for a clinical questionnaire and is mostly down to the fact that it takes two minutes and needs no equipment.
Scoring the Epworth Sleepiness Scale
Scoring the Epworth Sleepiness Scale is simple addition: each situation is worth 0, 1, 2 or 3 points, and the eight answers are summed for a total out of 24. There is no weighting and no adjustment for age or sex. The conventional interpretation of the total is:
- 0–10, normal. Ordinary daytime sleepiness. Most healthy adults land between 2 and 10.
- 11–14, mild excessive daytime sleepiness. Worth taking seriously, especially if it is new.
- 15–17, moderate excessive daytime sleepiness. This is the range where people describe fighting to stay awake at work.
- 18–24, severe excessive daytime sleepiness. Falling asleep in situations where it should be impossible. Worth a same-week appointment, and worth thinking hard about driving.
One result deserves more attention than the band it falls in: any sign that you could doze off while driving. That is the most alarming answer on the sheet, regardless of what the total says, because the same sleep pressure applies when the car is moving.
The score is also useful as a before-and-after measurement. If you start CPAP, change a medication, or finally fix a bedroom that was too warm, asking your doctor to repeat the questionnaire a month later gives you a number to compare rather than a vague sense that things are better.
What the Epworth Sleepiness Scale does not measure
It does not measure sleep apnea. This is the most common misreading of the score, and it cuts both ways. Plenty of people with moderate or severe obstructive sleep apnea score below 10, because habitual sleepiness gets normalised and because the scale depends on accurate self-assessment by someone whose judgement is itself impaired by poor sleep. In the other direction, a score of 16 is entirely compatible with having no breathing disorder at all and simply sleeping six hours a night on a rotating shift pattern.
It also does not distinguish between causes. Narcolepsy, insufficient sleep, depression, sedating antihistamines, restless legs, an undiagnosed thyroid problem and untreated apnea can all produce the same total. The scale says "this much sleepiness is present." It has nothing to say about why.
Finally, it measures a general recent tendency, not today. A single bad night will not move the score much, and it is not supposed to. If you want to know what happened last night specifically, that is a different question, and a questionnaire is the wrong instrument for it.
Neither questionnaire discussed on this page is a diagnosis. They are screening tools designed to help decide whether a proper assessment is worth arranging. A low score does not rule out a sleep disorder, and a high score does not confirm one. If you are sleepy enough to worry about driving, or someone has seen you stop breathing in your sleep, speak to a doctor rather than to a web page.
The STOP-BANG questionnaire: a different question
Where Epworth asks how sleepy you are, STOP-BANG asks how likely it is that obstructive sleep apnea is the reason. It mixes four things you can report, snoring, tiredness, observed breathing pauses, treated high blood pressure, with four physical risk factors: body mass index, age, neck size and sex. The acronym is the eight initials, and each yes is worth one point.
Frances Chung's group at the University of Toronto introduced the four-item STOP questionnaire in Anesthesiology in 2008 as a pre-operative screen, since undiagnosed apnea makes anaesthesia riskier, then added the four demographic items to sharpen it. The extended version was validated in British Journal of Anaesthesia in 2012, and a 2015 meta-analysis across surgical and sleep-clinic populations confirmed that it is good at the job it is built for: catching people who should be tested. It is deliberately over-inclusive. A high score flags a large group of people, most of whom will turn out to have something, but the point of a screen is to miss as few as possible rather than to be right about everyone.