We distributed a self-administered health questionnaire known as the Todai Health Index (THI) to a group of 191 women, aged 18-22 (average 19.7), who were at the time students in programs of nursing or public health nursing. This sample was divided into three groups on the basis of subject's answers to the question "Do you tend to go to sleep and get up early?" The subjects were classified as "early risers", "night owls" or "intermediates" according to their predilections . The THI yields

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... numerical scores assessing the degree of proneness to various conditions. We developed profiles of the groups using the t-test on the twelve scores as well as the discriminant values for the psychosomatic and neurotic scores. We would not be able to find out consistent trends which we hypothesized between the above question and the THI's twelve numerical scores and two discriminant values. Among the three groups, the intermediate group proved to be the most diffuse in the pattern of its daily cycles. It became clear that it would be difficult to compare the three groups directly. However, the THI's scale, "Irregularity of daily life" measuring the degree to which a person's life lacks a regular rhythm showed the highest degree of correspondence with the above typology. Taking the 25% who scored the highest on this measure and comparing them with the lowest 25%, we found that none of the former reported being early risers, and more reported waking late than those in the regular rhythm group. The regular rhythm group tended to report noticing fewer symptoms of physical or mental ailment. They tended to be emotionally more stable and calm, less prone to depression or anxiety and showed few signs of neurosis or psychosomatic illness.