Scores on morningness-eveningness and sleep habits of Korean students, Japanese students, and Japanese workers.

The Morningness-Eveningness Questionnaire and Life Habits Inventory were given to three groups of the same mean age: 533 Korean students, 468 Japanese students, and 311 Japanese workers. The distributions of scores on the questionnaire for these three groups are normal; however the Japanese students' distribution was slightly skewed towards the Evening type. The self-reported waking times and bedtimes for the three groups were late in the order of Morning, Intermediate, and Evening types. It is noteworthy, however, that the Korean students woke earlier than the Japanese students, and the workers always went to bed and woke earlier than the students. For the groups the variations in bedtime, waking time, and length of sleep were large, the sleep latency was long, and mood of the participants upon waking was bad in the order of the Morning. Intermediate, and Evening types. The scores of the Korean students were distributed more highly in the Morning type than were the Japanese students', but the students' sleep habits in both countries were quite similar. The subjects categorized as Evening types had more irregular sleep habits than those of the Morning type. In comparison with the student groups, Japanese workers of the same mean age had higher scores and slightly different sleep habits. The change in sleep habits could be seen as a result of the demands of employment, and the probable basis for difference in scores.