title: The Epworth Sleepiness Scale in Portuguese adults: from classical measurement theory to Rasch model analysis.
abstract: BACKGROUND
  The Epworth Sleepiness Scale (ESS) is a largely wide used scale for sleepiness assessment. Measurement properties are studied in a sample of Portuguese adults, using different statistical procedures.
  
  
  METHODS
  The sample consisted of 222 Portuguese adults (97 men and 125 women) with a mean age of 42 years old (SD = 12.5), 46 of which had obstructive sleep apnea (OSA) confirmed by polysomnography. The participants were assessed with the ESS, which was tested through a quantitative analysis based on the classical measurement theory (CMT) or the Rasch model (RM) conventions.
  
  
  RESULTS
  A principal component factor analysis was performed according to the CMT, revealing a single factor explaining 39.92% of the total variance of the scale. Internal consistency measured by Cronbach's α coefficient was of .77. The mean of inter-item correlation was of .31 (.05 < r > .47), whereas the item-total correlations were considered good (.46 < r > .73). The ESS total score for OSA patients was significantly higher than healthy participants (p < .05). Overall data from the RM analysis was consistent with the guidelines of Linacre and essential unidimensionality was empirically corroborated (61% the percentage of variance explained by the Rasch analysis). Model fit is adequate and the reliability coefficients for both items (.99) and subjects (.78) were considered good. The Cronbach's α coefficient was also satisfactory (.78).
  
  
  CONCLUSIONS
  The ESS showed an adequate structural, internal, and criterion validity, both in the CMT and the RM, suggesting this as a useful and effective measure for assessing sleepiness in Portuguese adults.
authors.affiliation: Escola de Psicologia e Ciências da Vida, Universidade Lusófona de Humanidades e Tecnologias and COPELABS, Campo Grande, 376, 1749-024, Lisboa, Portugal, p970@ulusofona.pt.
authors.forename: Paulo
authors.initials: P
authors.lastname: Sargento
authors.forename: Victoria
authors.initials: V
authors.lastname: Perea
authors.forename: Valentina
authors.initials: V
authors.lastname: Ladera
authors.forename: Paulo
authors.initials: P
authors.lastname: Lopes
authors.forename: Jorge
authors.initials: J
authors.lastname: Oliveira
mesh_terms: D000328:Adult; D000368:Aged; D003431:Cross-Cultural Comparison; D006970:Disorders of Excessive Somnolence / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D017286:Polysomnography / Q000706:statistics & numerical data*; D025341:Principal Component Analysis; D011594:Psychometrics / Q000706:statistics & numerical data*; D012016:Reference Values; D015203:Reproducibility of Results; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis*; D013223:Statistics as Topic; D011795:Surveys and Questionnaires