Confirmatory factor analysis of the Epworth Sleepiness Scale (ESS) in patients with obstructive sleep apnoea

Background: The Epworth Sleepiness Scale (ESS [Johns MW. A new method for measuring daytime sleepiness: the Epworth sleepiness scale. Sleep 1991;14(6):540–5]) has been used frequently to assess daytime sleepiness, particularly in the context of clinical sleep disorders. Its psychometric properties are still unclear, particularly when used to evaluate sleep propensity in patients with obstructive sleep apnoea. Methods: The present study used confirmatory factor analysis (CFA) to investigate a potential single-factor structure of the ESS in a sample of 759 Australian patients with a diagnosis of obstructive sleep apnoea by the treating physicians. Results: CFA results from showed that the original single-factor structure proposed by Johns [Johns MW. Reliability and factor analysis of the Epworth Sleepiness Scale. Sleep 1992;15(4):376–81] did not adequately fit the data. A re-specified single-factor solution provided a good fit for data, and this improved fit was confirmed on a second CFA. Conclusions: The findings suggest that standard scoring of the ESS should be interpreted cautiously for patients with obstructive sleep apnoea.