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A New Method for Measuring Daytime Sleepiness - The Epworth Sleepiness Scale

A New Method for Measuring Daytime Sleepiness - The Epworth Sleepiness Scale - Clinical Hub, UW Health Clinical Tool Search, UW Health Clinical Tool Search, Questionnaires, Related

Sleep, 14(6):540--545
' 1991 American Sleep Disorders Association and Sleep Research Society
A New Method for Measuring Daytime Sleepiness:
The Epworth Sleepiness Scale
Murray W. Johns
Sleep Disorders Unit, Epworth Hospital, Melbourne, Victoria, Australia
Summary: 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 genera1level 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 distin›
guished 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 Sa0
recorded overnight. ESS scores of patients who simply snored did not differ from controls. Key Words: Sleepiness›
Questionnaire-Sleep propensity-Insomnia-Obstructive sleep apnea syndrome.
A large proportion of adult patients who present to
sleep disorder centers have disorders associated with
excessive daytime sleepiness. These include obstmc›
tive sleep apnea syndrome (OSAS), periodic limb
movement disorder (PLMD), narcolepsy, idiopathic
hypersomnia and other miscellaneous disorders (I).
The severity of their chronic daytime sleepiness is an
important aspect of each patient’s assessment. Thus,
there is a great need for a simple standardized test for
measuring a patient’s general level of sleepiness, which
is independent of short-term variations in sleepiness,
with the time of day and from day to day.
The multiple sleep latency test (MSLT) is widdy
used and is generally believed to provide a valid mea›
surement of sleepiness on the particular day of the test
(2,3). It is based on the premise that the sleepier lthe
subject, the quicker he will fall asleep when encouraged
to do so while lying down in a non stimulating envi›
ronment. The MSLT has a reasonably high test-retest
reliability over periods of months in normal subjects
(4). Assuming the same reliability holds tme for pa›
tients, the MSLT must be considered the standard
method for measuring their chronic daytime sleepi›
ness. However, the MSLT is very cumbersome, time-
Accepted for publication July 1991.
Address correspondence and reprint requests to Dr. Murray w.
Johns, Sleep Disorders Unit, Epworth Hospital, Melbourne, Victoria
3121, Australia.
consuming and expensive to perform. It takes all day,
both for the subject and the polysomnographer and is
not easy to justify as a routine test for all patients.
Other measures of sleepiness have been devised (5,6).
In the maintenance of wakefulness test (MWT) the
latency to sleep onset is measured with the subject
sitting in a dimly lit, warm, quiet room, trying to stay
awake rather than to fall asleep (5). However, all such
tests share the disadvantage of the MSLT in being
cumbersome and expensive. Similar criticisms can be
levelled at tests of sleepiness based on pupillometry
(7), or cerebral evoked potentials (8). Other assess›
ments of sleepiness have involved prolonged psycho›
motor performance tests, the results of which are not
related in any simple or consistent way to sleepiness
in different subjects (9).
By contrast, the Stanford sleepiness scale (SSS) is a
quick and simple test (l0). It involves the subject’s
own reports of symptoms and feelings at a particular
time. Visual analogue scales (V AS) of sleepiness/al›
ertness have also been used in this context (11). How›
ever, these tests do not attempt to measure the general
level of daytime sleepiness, as distinct from feelings of
sleepiness at a particular time. Nor, it appears, is the
subjective sleepiness that they measure the same as the
objective sleepiness measured by the MSLT (3,7).
Scores on the SSS or on a VAS of sleepiness are not
significantly correlated with sleep latency in the MSLT,

TABLE 1. The Epworth sleepiness scale
Today’s date: Your age (years): ___ _
Your sex (male = M; female = F): _________ _
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 oflife 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:
o = would never doze
I = slight chance of dozing
2 = moderate change of dozing
3 = high chance of dozing
Sitting and reading
Watching TV
Sitting, inactive in a public place (e.g. a theater or a
As a passenger in a car for an hour without a break
Lying down to rest in the afternoon when circumstanc-
es permit
Sitting and talking to someone
Sitting quietly after a lunch without alcohol
In a car, while stopped for a few minutes in the traffic
Thank you for your cooperation
even when measured at virtually the same time (12).
These subjective reports may be related more to tired›
ness and fatigue than to sleep propensity, as manifested
by the tendency to fall asleep.
The present report describes the development and
use of a new questionnaire, the Epworth sleepiness
scale (ESS), designed to measure sleep propensity in a
simple, standardized way. The scale covers the whole
range of sleep propensities, from the highest to the
Development of the ESS
The concept of the ESS was derived from observa›
tions about the nature and occurrence of daytime sleep
and sleepiness. Some people who suffer from excessive
daytime sleepiness keep themselves busy and choose
not to lie down nor to sit and relax during the day,
thereby purposely avoiding daytime sleep. Others who
may be bored, with spare time or who are socially
withdrawn but who may not be very sleepy, choose to
lie down and sleep during the day. About 50% of os›
tensibly healthy medical students usually sleep during
the day at least once in an average week (13). Among
17-22-year-old recruits entering the French army, 19%
reported sleeping during the day, regularly or occa›
sionally. But only 5% complained of daytime sleepi-
ness (14). Thus, knowing how frequently or for how
long subjects usually sleep during the day will probably
not provide a useful measurement of their sleepiness.
By contrast, sleepy people often describe how they
doze off inadvertently while engaged in activities that
involve low levels of stimulation, relative immobility
and relaxation, such as sitting and watching TV. Earlier
questionnaire surveys have indicated which situations,
commonly encountered in daily life, are the most sopo›
rific (15). A large survey among adults in New Mexico
asked about their frequency of falling asleep in five
situations (16). The authors derived a score from the
three "most sleepy" questions, which referred to falling
asleep while "inactive in a public place", "at work",
and "in a moving vehicle as passenger or driver".
MSLTs on 116 of these subjects showed a statistically
significant correlation between their sleep latency (SL)
and their answers to those three questions (r = -0.32,
p < 0.001).
The ESS is based on questions referring to eight such
situations, some known to be very soporific; others less
so. The questionnaire, which is self-administered, is
reproduced in Table 1. Subjects are asked to rate on a
scale of 0-3 how likely they would be to doze off or
fall asleep in the eight situations, based on their usual
way of life in recent times. A distinction is made be›
tween dozing off and simply feeling tired. If a subject
has not been in some of the situations recently, he is
asked, nonetheless, to estimate how each might affect
The ESS tries to overcome the fact that people have
different daily routines, some facilitating and others
inhibiting daytime sleep. For example, the ESS does
not ask how frequently the subject falls asleep while
watching TV. That would depend on how frequently
he watched TV as much as on his sleepiness. Instead,
the subject rates the chances that he would doze off
whenever he watches TV.
One question asks how likely the subject would be
to doze off while lying down to rest in the afternoon
when circumstances permit. It was felt that normal
people probably would, and sleepy people certainly
would tend to doze off in that situation. Never to do
so would indicate an unusually low level of sleepiness,
as described by some insomniacs. Some other situa›
tions were included in the questionnaire because it was
believed that only the most sleepy people.would doze
in them - while sitting and talking to someone, and in
a car while stopped for a few minutes in traffic. These
suppositions proved correct.
The numbers selected for the eight situations in the
ESS were added together to give a score for each sub›
ject, between 0 and 24. These ESS scores proved ca›
pable of distinguishing individuals and diagnostic
groups over the whole range of daytime sleepiness.
Sleep. Vol. 14, No.6, 1991

TABLE 2. The groups of experimental subjects, their ages and ESS scores
Normal controls
Primary snoring
. Narcolepsy
Idiopathic hypersomnia
Total number of subjects
30 (14/16)
32 (29/3)
55 (53/2)
13 (8/5)
14 (8/6)
18 (16/2)
A total of 180 adult subjects completed the qUI~s­
tion~aire. There were 30 controls who were mainly
hospItal employees, working during the day, who gave
a history of normal sleep habits without snoring. There
were 150 patients with various sleep disorders, whose
ages, sex and diagnostic categories are shown in Table
2. Every new patient who presented to the Epworth
Sleep Disorders Unit answered the ESS at their first
consultation. After investigation, all patients with the
diagnoses listed in Table 2 were included in the study
until there were 150. The ages of patients ranged from
18 to 78 years. The mean age within diagnostic groups
varied from 36 to 52 years. Men greatly outnumbered
women in the snoring, OSAS and PLMD groups. The
sexes were about equal in the other groups, apart from
the insomniacs where women outnumbered men.
A total of 138 patients had overnight polysomnog›
raphy, but another 12 who were clearly suffering from
either chronic psychophysiological or idiopathic lin›
somnia did not. The latter diagnoses were made on the
basis of each patient’s history, using the criteria set out
in the International Classification of Sleep Disordl~rs
(1). Other insomniacs, with mood disorders or drug
effects, were excluded.
Twenty-seven patients had MSLTs after overnight
polysomnography. They had four naps, at 1000, 1200,
1400 and 1600 hours. Sleep latency was measured from
the time lights were switched off until the onset of stage
1 sleep of at least 1 minute duration, or the onset of
either stage 2 or rapid eye movement (REM) slec!p.
The early onset of REM sleep was indicated by the
occurrence of REM sleep within 20 minutes of sle:ep
onset. Of the 27 patients, 11 had narcolepsy diagnosed
from the patient’s history, particularly of cataplexy,
associated with an SL of less than 10 minutes and the
early onset of REM sleep in two or more naps (10
patients) or in one nap (1 patient with cataplexy). Four›
teen of the 27 patients had idiopathic hypersomnia,
diagnosed from their excessive daytime sleepiness in
the absence of either cataplexy or the early onset of
REM sleep in the MSLT. The remaining two patients
Sleep, Vol. 14. No.6, 1991
Age in years ESS scores
(mean + SD)
(mean + SD) Range
36.4 – 9.9 5.9 – 2.2 2-10
45.7 – 10.7 6.5 – 3.0 0-11
48.4 – 10.7 11.7 – 4.6 4-23
46.6 – 12.0 17.5 – 3.5 13-23
41.4 – 14.0 17.9–3.1 12-24
40.3 – 14.6 2.2 – 2.0 0-6
52.5 + 10.3 9.2 + 4.0 2 16
had excessive daytime sleepiness due to OSAS. The
ESS scores for the 27 patients who had MSLTs ranged
from 11 to 24.
All patients with primary snoring had presented ini›
tially because of the intensity and persistence of their
snoring, on most nights at least. Many had been ob›
served .at home to pause in their breathing at night,
su~estmg that they may have had sleep apnea, but
thIS was found not to be of clinical significance by
polysomnography. The respiratory disturbance index
(RDI) was calculated as the number of apneas and
hypopneas causing a drop of > 3% in the arterial ox›
ygen saturation per hour of sleep. The RDI for primary
snorers was ::55. The 55 patients with OSAS were di›
vided into three subcategories according to their RDI,
regardless of their complaints about daytime sleepiness
or insomnia (Table 3). The RDI for mild OSAS was
within the range> 5-15; for moderate OSAS the range
was > 15-30, and for severe OSAS it was > 30.
A diagnosis of PLMD was made only if there were
at least 90 separate movements in one or both legs per
night. The mean periodic movement index for these
subjects, calculated as the number of movement events
per hour of sleep, was 43.6 – 30.4 (SD). Patients who
had both PLMD and OSAS were excluded from this
study. However, 9 of the 18 subjects with PLMD snored
during polysomnography without having OSAS.
Statistical methods
The ESS scores of male and female control subjects
were compared by a Student’s t test. Differences in ESS
scores between the diagnostic groups were tested by
one-way ANOY A and then by posthoc ScheWe tests.
A separate ANOY A and posthoc ScheWe tests were
TABLE 3. ESS scores in mild, moderate and severe OSAS
Moderate OSAS
Severe OSAS
8.8 – 2.3
21.1 – 4.0
49.5 + 9.6
number of
22 (21/1)
20 (20/0)
13 (12/1)
ESS scores
(mean – SD) Range
9.S – 3.3 4-16
11.5 – 4.2 5-20
16.0 + 4.4 8 23

used to test the differences in ESS scores between pri›
mary snorers and the three categories of OSAS. The
ScheWe test is conservative and is suitable for groups
with unequal numbers of subjects (17). The distribu›
tion of sleep latencies ,measured in minutes, was highly
skewed positively and was normalized by log., trans›
formation. The relationships between pairs of contin›
uous variables, such as RDI and sleep latency during
overnight polysomnography, were tested by Pearson
correlation coefficients and linear regression. Statistical
significance was accepted at p < 0.05 in two-tailed
The mean ESS score for control subjects was 5.9 –
2.2 (SD) and their modal score was 6. There was no
significant difference in the scores between male and
female controls (males = 5.64 – 2.56; females = 6.06
– 1.84, t = 0.520, p = 0.607). Consequently, no dis›
tinction was made between the sexes in other groups.
Patients suffering from disorders known to be as›
sociated with excessive daytime sleepiness reported the
likelihood of dozing under circumstances that were not
conducive to sleep in normal subjects. For example,
96% of the patients with either narcolepsy or idiopathic
hypersomnia reported some chance, and often a high
chance, of dozing while sitting and talking to someone,
or in a car while stopped for a few minutes in the traffic.
Only 6% of controls reported a slight chance of doing
Patients with persistent psychophysiological or idio›
pathic insomnia reported either a complete inability
or only a slight chance of dozing while lying down to
rest in the afternoon when circumstances permitted.
By contrast, 94% of controls reported some likelihood
of dozing then.
One-way ANOV A demonstrated significant differ›
ences in ESS scores between the seven diagnostic groups
in Table 2 (F= 50.00; df= 6,173; p < 0.0001). Posthoc
tests between paired groups showed that the ESS scores
for primary snorers did not differ from controls (p =
0.998). Scores for OSAS, narcolepsy and idiopathic
hypersomnia were significantly higher than for controls
(p < 0.001) or primary snorers (p < 0.001). The in›
somniacs had significantly lower scores (p < 0.01) than
all groups other than controls, for which the difference
did not quite reach statistical significance (p = 0.063).
The ESS scores of patients with PLMD did not differ
significantly from controls (p = 0.149).
A separate one-way ANOV A for the ESS scores of
primary snorers and the three subcategories of OSAS
showed significant differences between these groups (F
= 23.11; df = 3,82; p < 0.001). Posthoc tests then
showed that ESS scores for each level of OSAS were
significantly higher than for primary snorers (p = 0.035
for mild OSAS; p < 0.001 for moderate and severe
OSAS). Scores for severe OSAS were higher than for
moderate OSAS (p < 0.001), but the difference be›
tween mild and moderate OSAS did not reach statis›
tical significance (p = 0.085).
Considering a1155 patients with OSAS together, there
was a significant correlation, on the one hand, between
ESS scores and RDI (r = 0.550, p < 0.001) and on the
other hand, between ESS scores and the minimum
recorded during apneas overnight (r = -0.457,
p < 0.001). The RDI and the minimum overnight Sa0
during apneas were also significantly correlated (r =
-0.687, p < 0.001). The linear regression equations
for these three relationships, in the form Y = a + bx,
were as follows:
(RDI) = -0.674 + 2.006(ESS score)
(minimum Sa02%) = 86.47 - 1.055(ESS score)
(minimum Sa0
%) = 84.15 - 0.440(RDI)
Among the 138 patients who had overnight poly›
somnography there was a significant correlation be›
tween ESS score and (In) sleep latency at night (r =
-0.379, n = 138, p < 0.001). In the smaller group of
patients who had MSLTs, the correlation between In
(SL) during the day and ESS score was also statistically
significant (r = -0.514, n = 27, p < 0.01. The linear
regression equation for this relationship was In (SL) =
3.353 - 0.091(ESS score).
Individual ESS scores of 16 or more, indicating a
high level of daytime sleepiness, were found only in
patients with narcolepsy, idiopathic hypersomnia or
OSAS of at least moderate severity (i.e. RDI > 15).
All patients with either narcolepsy or idiopathic hy›
persomnia had higher ESS scores than the controls (i.e.
ESS > 10) as did 12 of 13 patients with severe OSAS.
The remaining patient in the latter category had an
ESS score of 8 and was clinically not much affected by
his sleep apnea.
Within the group of patients with PLMD, the pe›
riodic movement index, which ranged from 16 to 122
movements per hours of sleep, was not significantly
correlated with ESS scores (r = 0.049, n = 18, p >
These results provide evidence that a questionnaire›
based scale as brief and as simple as the ESS can give
valid measurements of sleep propensity in adults. ESS
scores significantly distinguished groups of patients who
are known from other investigations to have differ›
ences in their levels of sleepiness, as measured by the
MSLT (2,18). ESS scores were significantly correlated
Sleep. Vol. 14. No.6. 1991

with sleep latency measured during the day with MSLTs
and at night with polysomnography. This is despite
any effect of the first night in the laboratory. Others
have found a significant positive correlation between
the SL at night and during the day in the same subject
ESS scores greater than 16, indicative of a high level
of daytime sleepiness, were encountered only in pa›
tients with moderate or severe OSAS (RDI > 15),
narcolepsy or idiopathic hypersomnia. These disorders
are known to be associated with excessive daytime
sleepiness as measured by the MSLT (2,18). Newr›
theless, high ESS scores, by themselves, are not diag›
nostic of a particular sleep disorder, any more than is
an SL of 5 minutes in an MSLT.
ESS scores were correlated with both the RDI and
the minimum Sa0
recorded during polysomnography
in patients with OSAS of differing severity. In the past,
these measures of the severity of OS AS have been found
to be related to the SL in MSLTs in some, but not in
all investigations (18,20). The finding that ESS scores
can distinguish patients who simply snore from those
with even mild OSAS is evidence for the sensitivity of
the ESS. The questionnaire should be useful in eluci›
dating the epidemiology of snoring and OSAS, and any
associated cardiovascular or cerebrovascular risks.
Previous investigations of this kind have tended to blur
the distinction between primary snoring and OSAS
In the patients with PLMD, the finding of an almost
zero correlation between their periodic movement in›
dex and ESS scores suggests that whatever level of
daytime sleepiness is associated with PLMD, it is not
related simply to the frequency oflimb movements. It
may be more closely related to the frequency of those
movements producing arousal rather than those that
do not. This distinction was not made here and further
investigation is required to clarify this relationship.
The low ESS scores of patients with idiopathic or
psychophysiological insomnia are consistent with ev›
idence that such patients have a low sleep propensity,
even when they are able to relax (22). It must not be
assumed, however, that this is necessarily so for other
kinds of insomnia, such as with mood disorders.
The relatively wide range ofESS scores in the control
subjects [2-10] is consistent with evidence that some
healthy adults, without recognizable sleep disordt~rs,
remain sleepier than others during the day (23). Such
differences persist in MSLTs, even after extending the
hours of nocturnal sleep to overcome possible sleep
deprivation (24). The sleep propensity of a subject on
a particular day would be influenced by the quality and
duration of prior sleep or of sleep deprivation, the time
of day, the presence of various sleep disorders, drug
effects, the level of interest and motivation induced by
Sleep, Vol. 14, No.6, 1991
the situation at hand, as well as longer-term physio›
logical differences. The ESS does not distinguish the
nature oflong-term physiological or pathological pro›
cesses that produce a particular level of sleep propen›
sity. Other investigations, including overnight poly›
somnography, are required for that.
The ESS assumes that subjects can remember wheth›
er or not and under what circumstances they have
dozed off during the day as part of their "usual way of
life in recent times". The present results suggest that
most patients can give meaningful self reports about
this aspect of their behavior and that their ESS scores
provide a measurement of their general level of day›
time sleepiness, from low to very high levels. This has
not been achieved previously by any other published
Acknowledgement: Irene Lehel assisted with the admin›
istration of questionnaires to the control subjects.
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