title: Evaluation of two circadian rhythm questionnaires for screening for the delayed sleep phase disorder.
abstract: OBJECTIVE
  Delayed sleep phase disorder (DSPD) is a condition in which patients often fall asleep some hours after midnight and have difficulty waking up in the morning. Circadian chronotype questionnaires such as Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) and Basic Language Morningness (BALM) scale have been used for screening for DSPD. This study was to evaluate these two chronotype questionnaires for screening of DSPD.
  
  
  METHODS
  The study samples were 444 DSPD and 438 controls. Cronbach's alpha coefficient was calculated to evaluate for internal consistency. An exploratory factor analysis was conducted using principal-axis factoring. The diagnostic performance of a test was evaluated using Receiver Operating Characteristic (ROC) curve analysis. A discriminant function analysis was also performed.
  
  
  RESULTS
  For internal consistency, Cronbach's alpha of 0.898 for BALM was higher than the 0.837 for MEQ, though both have acceptable internal consistency. BALM has better construct validity than the MEQ because some MEQ items measure different dimensions. However, when we evaluated the efficiency of two questionnaires for DSPD diagnosis by using the ROC curve, the BALM was similar to the MEQ. In a discriminant analysis with the BALM to classify the two groups (DSPD vs. normal), 6 items were identified that resulted in good classification accuracy. Upon examination of the classification procedure, 94.2% of the originally grouped cases were classified correctly.
  
  
  CONCLUSIONS
  These findings suggest that the BALM has better psychometric properties than the MEQ in screening and discriminating DSPS.
authors.affiliation: Department of Psychology, Gyeongsang National University, Jinju, Republic of Korea.
authors.forename: Min Kyu
authors.initials: MK
authors.lastname: Rhee
authors.forename: Heon-Jeong
authors.initials: HJ
authors.lastname: Lee
authors.forename: Katharine M
authors.initials: KM
authors.lastname: Rex
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Kripke