This study evaluates the psychometric properties and assesses the test-retest reliability and longer-term stability of scores on the Circadian Type Questionnaire (CTQ) of Folkardet al. (1979) in a sample of 445 students. The scales were found to lack internal consistency and the factor structure originally proposed was not replicated. Cultural variation in CTQ scores was suggested. Test-retest reliability, over three months in a subgroup of 36, was poor for the V and M scales. Longer-term stability, over nine months in a subgroup of 36 who were exposed to shiftwork, was better but significant decreases were found in rigidity of sleeping habits (Rs) and morningness (M) scores. A factor analysis suggested that the scales should be constructed differently; however, the properties of such scales were still not optimal. The CTQ has psychometric flaws and needs to be improved before it could be expected to reliably function as a predictive test of adaptation to shiftwork.
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