Psychometric evaluation of the Early/Late Preferences Scale

This paper examines the psychometric quality of the Early/Late Preferences Scale (PS) relative to that of the Composite Morningness Scale (CS). Questi onnaires were completed by 670 undergraduate students aged 16-37 years (mea n 22.5), of whom 64% were female. Both scales displayed satisfactory inter- item correlations and similar total mean scores to those reported previousl y, although the CS had higher variability. Principal axis factor analysis p roduced single-factor solutions for both scales, although loadings for Item s 7 and 9 on the PS were low. Internal consistencies for both scales were g ood (PS=0.86, CS=0.90) with only a small improvement achieved by deleting I tems 7 and 9 from the PS. Test-retest reliability over 11 weeks was good fo r both scales (PS=0.92, CS=0.89). Differences between morning, evening and intermediate groups in self-rated alertness at different times of day, and significant correlations with other indices of morning-evening orientation, provided evidence of validity for both scales. These results indicate that PS is psychometrically comparable with CS. In view of its simpler format a nd lower cultural specificity, PS may be considered a preferable measure fo r most applications.