Factor Analysis of the Insomnia Severity Index and Epworth Sleepiness Scale in Shift Workers

BACKGROUND: Over one million Korean night shift workers undergo clinical assessment of sleep using the Insomnia Severity Index (ISI) and Epworth Sleepiness Scale (ESS) by occupational medical examination each year. Therefore, this study was conducted to evaluate the reliability and validity of the ISI and ESS using occupational medical examination data. METHODS: The study subjects included 12,056 shift workers at an electronics company who underwent an occupational health examination about shift work in 2018. The evaluation of the ISI and ESS was performed using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). RESULTS: According to the results of the EFA, the ISI had a single-factor structure, while the ESS had a two-factor structure, which was inconsistent with the findings of previous studies. The results of the EFA of 15 items from the combined ISI and ESS suggested a three-factor structure, with one factor for ISI items and two factors for ESS items, while the results of the CFA suggested sufficient validity of the combination of the ISI and ESS for sleep evaluation. CONCLUSION: The results suggest that the ISI and ESS have sufficient reliability and validity to be used for occupational health examinations about shift work.