Development of a Japanese version of the Epworth Sleepiness Scale (JESS) based on Item Response Theory

Misa Takegami, Yoshimi Suzukamo, Takafumi Wakita, Hiroyuki Noguchi, Kazuo Chin, Hiroshi Kadotani, Yuichi Inoue, Yasunori Oka, Takaya Nakamura, Joseph Green, Murray W. Johns, Shunichi Fukuhara

Research output: Contribution to journalArticlepeer-review

233 Citations (Scopus)


Background. Various Japanese versions of the Epworth Sleepiness Scale (ESS) have been used, but none was developed via standard procedures. Here we report on the construction and testing of the developer-authorized Japanese version of the ESS (JESS). Methods. Developing the JESS involved translations, back translations, a pilot study, and psychometric testing. We identified questions in the ESS that were difficult to answer or were inappropriate in Japan, proposed possible replacements for those questions, and tested them with analyses based on item response theory (IRT) and classical test theory. The subjects were healthy people and patients with narcolepsy, idiopathic hypersomnia, or obstructive sleep apnea syndrome. Results. We identified two of our proposed questions as appropriate replacements for two problematic questions in the ESS. The JESS had very few missing data. Internal consistency reliability and test-retest reliability were high. The patients had significantly higher JESS scores than did the healthy people, and higher JESS scores were associated with worse daytime function, as measured with the Pittsburgh Sleep Quality Index. Conclusions. In Japan, the JESS provides reliable and valid information on daytime sleepiness. Researchers who use the ESS with other populations should combine their knowledge of local conditions with the results of psychometric tests.

Original languageEnglish
Pages (from-to)556-565
Number of pages10
JournalSleep Medicine
Issue number5
Publication statusPublished - 2009 May


  • Daytime sleepiness
  • Epworth Sleepiness Scale
  • Item Response Theory
  • Psychometric propensities
  • Reliability
  • Validity


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