A questionnaire was developed to distinguish between people who differed in the degree to which their circadian rhythms adjusted to night work. This was administered to 48 #x2018; permanent #x2019; night nurses taking part in a large shift work study. Factor analyses indicated that there were three main factors. These were (I) rigidity/flexibility of sleeping habits, (ii) ability/inability to overcome drowsiness, and (iii) morningness/eveningness. Correlations were computed between the nurses'scores on each of these factors and a range of measures of adjustment of circadian rhythm. A number of significant correlations were found with both psychological and physiological measures, thus indicating that the factors had at least concurrent validity. It is concluded that it may prove feasible to develop a questionnaire that would predict the degree to which people's rhythms would adjust to shift work, and that flexibility of sleeping habits and the ability to overcome drowsiness should be components of such a questionnaire.
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