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A questionnaire was distributed to 300 students and 175 workers of the same mean age to determine their morningness-eveningness preferences. Morning and evening type samples obtained from these larger populations were requested to keep logs of bed and rising time for each day of a 2 week period. In comparison to students, workers had a distribution significantly skewed towards the morningness scores. Differences were found between the expressed preferences and the sleep-waking diary data in workers, but not in students. The acquisition of a regular job seems to induce a change in sleep-wake behaviour, particularly in evening workers.
Mecacci et al. (Thu,) studied this question.