Epworth sleepiness scale: A meta-analytic study on the internal consistency

Abstract

Objective/background: The Epworth Sleepiness Scale (ESS) is one of the most used self-reported instruments to assess sleepiness. Thus, several adaptations into different Languages have been performed worldwide over the years. The scale has produced disparate psychometric properties when applied in different settings. In the current study, our aim was to perform a Reliability Generalization meta-analysis of the Cronbach᾽s alphas of all published studies on ESS, specifically with a psychometric focus.

Patients/methods: Three reference databases (Scopus, PubMed and Web of Science) were searched since 1991 to October 2022 and all the records on psychometric or validation studies that reported Cronbach's alphas, from clinical and nonclinical groups, were included. In total, data from 46 publications (63 estimates) were extracted, comprising 92,503 participants.

Results: Using a Random-Effects Model, the cumulative Cronbach's alpha for the 63 estimates was about 0.82 (CI: 0.798, 0.832) which can be considered as a good measure. However, and as expected, it was observed a high level of heterogeneity (I² = 98.96%). Moderation analyses considering setting, date, continent, risk of bias, sex, age and language were performed in order to account for the heterogeneity. Even so, only the variables study setting and continent were significant, and had little importance in explaining the heterogeneity.

Conclusions: The ESS is a reliable tool to measure sleepiness; however, further studies are needed to investigate what variables might explain the observed variability. Moreover, it will be important to include empirical studies beyond psychometric ones.

Keywords: Cronbach's alpha; Epworth sleepiness scale; Meta-analysis; Reliability generalization; Sleep; Systematic review.