Focus area: Daytime sleepiness
Overview: Dr Johns first developed the Epworth Sleepiness Scale (ESS) for adults in 1990 and subsequently modified it slightly in 1997. He developed it so he could assess the ‘daytime sleepiness’ of the patients in his own private practice of Sleep Medicine. He named the questionnaire after Epworth Hospital in Melbourne, where he established the Epworth Sleep Centre in 1988.
Total number of items: Eight
Administration: Self-report
Standardized cadence: Weekly
Estimated completion time: Two to five minutes
Supported subscales: None
Age range: 18+
Scoring and interpretation: The ESS score (the sum of 8 item scores, 0-3) can range from 0 to 24. The higher the ESS score, the higher that person’s average sleep propensity in daily life (ASP), or their ‘daytime sleepiness’.
Reliability/Validity: The internal consistency of responses to the eight questions has been tested by Cronbach’s alpha, which has varied between 0.73 and 0.90 (mean = 0.82) in ten separate investigations (eg. Johns,1992; Hagell et al, 2007). The test-retest reliability of ESS scores (measured over a few weeks to a few months) has been tested by the intraclass correlation coefficient which has varied between 0.81 and 0.93 in five separate investigations (eg. Gibson et al. 2006; Izci et al. 2007; Cho et al 2011; van der Heide et al. 2015).
Principal components analysis of ESS item-scores has yielded variable results, with a single factor in some investigations, but more than one factor in others. In the latter investigations there has been one dominant factor, as well as one or two minor factors with Eigenvalues not much above 1.0, the assumed cut-off point (eg. Johns, 1992; Sargento et al, 2013). We might conclude that there is one dominant factor, with high loadings on all scales, but sometimes there are additional minor factors that vary between groups.
Additional information: The ESS asks the respondent to rate on a 4-point scale (0-3) their usual chances of having dozed off or fallen asleep while engaged in eight different activities that differ widely in their somnificity. These ESS item-scores provide estimates of eight different SSPs for that person (Johns, 1994; 2010). The total ESS score (the sum of 8 item-scores) gives an estimate of a more general characteristic, the person’s ‘average sleep propensity’ or ASP, across a wide range of activities in their daily lives (Johns, 2002). There is no other measure of ASP available at present with which to compare ESS scores directly.
The ESS does not ask about the person’s subjective feelings of alertness/drowsiness at some particular time, as measured by the Karolinska Sleepiness Scale. Nor does it measure how often, or for how long, the respondent sleeps during the day. The ESS is not a check-list for identifying those situations in which the respondent most frequently dozes during the day. Nor can it measure a person’s level of alertness/drowsiness continuously, as Optalert technology does (Johns, 2008; Anderson et al, 2013).
The ESS specifically distinguishes reports of dozing behaviour (and estimates of SSPs) from feelings of fatigue and drowsiness/sleepiness, in the sense of ‘weariness from exertion’. Fatigue and drowsiness/sleepiness are related concepts that are often confused (Johns 2000(a), 2003, 2009; Mairesse et al, 2016).