J.L. Terry, D.P. Heil FACSM

Montana State University, Bozeman, MT

The Epworth Sleepiness Scale (ESS) is a survey designed to assess daytime dysfunction due to sleepiness in both clinical and healthy populations. Research has reported that nighttime sleep quality, as well as daytime sleepiness, can amplify the perception of psychological stressors, as well as delay recovery from physical stress (i.e., training). A new study from our lab plans to use the ESS as part of a battery of surveys aimed to better understand the contribution of daytime sleepiness, and other potential stressors, to the development of chronic psychophysiological stress. Thus, assessing the test-retest reliability of the ESS will help to determine the repeatability of this tool in a non-clinical population. PURPOSE: This study investigated the test-retest reliability of the ESS in healthy adults. METHODS: Nineteen participants (Mean±SD: 13 women, 29±11 years; 6 men, 38±15 years) completed an online survey containing the ESS, as well as other questions related to stress and sleep quality. Questions were presented in a random order to each participant on two separate occasions during the same day and at least one hour apart. The ESS is a short collection of questions that asks subjects to rate (using a 4-point scale with 0-3 range) the chance that they will fall asleep or doze off during 8 common daily activities (e.g., watching TV, sitting in a car while stopped at a traffic light). The scores for the 8 questions are then summed into a single sleepiness global score (GS). Test-retest reliability was assessed using 2-factor repeated measures ANOVA (0.05 alpha), the intraclass correlation coefficient (ICC) and the standard error of measurement (SEM). Both ICC and SEM were calculated for 2-trial (k=2) and 1-trial (k=1) reliability. RESULTS: On a scale of 0-24, the GS ranged from 0 to 11 (Mean±SD: 6±3) in this population of healthy adults. No significant differences were observed between trials (P = 0.35) with a 2-trial ICC of 0.65 (0-1 scale) and SEM of ±1.9 indicating moderate reliability. When extrapolated to single trial reliability, an ICC of 0.48 and SEM of ±2.3 were weaker but still indicating a moderate level of reliability. CONCLUSIONS: The ESS is a moderately reliable measure of daytime sleepiness in healthy adults. The repeatability of the ESS is sufficient to justify its use in our upcoming study investigating the contribution of daytime sleepiness, among other variables, to chronic stress development.

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