Reliability and Factor Analysis of the Epworth Sleepiness Scale

TLDR

The Epworth Sleepiness Scale is a self‑administered eight‑item questionnaire proposed as a simple method for measuring daytime sleepiness in adults. This study examined the reliability and internal consistency of the ESS. The ESS showed high test‑retest reliability (r = 0.82) in healthy students, reduced scores after CPAP treatment in OSA patients, strong internal consistency (Cronbach’s α = 0.88), a single‑factor structure in both groups, and overall proved to be a simple, reliable tool for assessing persistent daytime sleepiness.

Abstract

The Epworth Sleepiness Scale (ESS) is a self-administered eight-item questionnaire that has been proposed as a simple method for measuring daytime sleepiness in adults. This investigation was concerned with the reliability and internal consistency of the ESS. When 87 healthy medical students were tested and retested 5 months later, their paired ESS scores did not change significantly and were highly correlated (r = 0.82). By contrast, ESS scores that were initially high in 54 patients suffering from obstructive sleep apnea syndrome returned to more normal levels, as expected, after 3–9 months' treatment with nasal continuous positive airway pressure. The questionnaire had a high level of internal consistency as measured by Cronbach's alpha (0.88). Factor analysis of item scores showed that the ESS had only one factor for 104 medical students and for 150 patients with various sleep disorders. The ESS is a simple and reliable method for measuring persistent daytime sleepiness in adults.