A diurnal type scale. Construction, consistency and validation in shift work.

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Abstract
The purpose of the study was to construct a short scale with high internal reliability for use as a measure of diurnal type (morning or evening disposition), to validate the constructed index against sleep/wake behavior in connection with different work hours, to study inter- and intraindividual consistency over a 1 yr interval and to examine the effects of changed work hours on diurnal type scores. Shift workers (300) filled out the same questionnaire twice with a 1 yr interval. An index of 7 items was constructed yielding a Cronbach .alpha. coefficient of 0.75. Analysis showed that morning active (MA) individuals rose earlier and went to bed earlier than evening active (EA) individuals and the former had a longer sleep length than the latter during days with a morning shift, while the opposite was true for afternoon and night shifts. During days with a morning shift more EA individuals took naps but during days with a night shift the MA group took naps more often than the EA group. MA individuals had fewer sleep complaints than EA individuals during the morning shift. The correlation was high (r = 0.79, P < 0.001) for the index between the 2 administrations with a 1 yr interval. Those who had changed from shift work to day work reported a more pronounced morning active disposition. Interindividual consistency was still pronounced. The analysis resulted in a short diurnal type scale with high internal reliability and high consistency between measurements and it differentiated between morning and evening types in sleep/wake habits.

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