Background: In the current Japanese payment system for the treatment of psychiatric inpatients, the length of hospital stay and nurse staffing levels are key determinants of the amount of payment. These factors do not fully reflect the costs of care for each patient. The objective of this study was to clarify the relationship between patient characteristics and their care costs as measured by "care time" for patients with schizophrenia. Methods: Patient characteristics and care time were investigated in 14,557 inpatients in 102 psychiatric hospitals in Japan. Of these 14,557 inpatients, data for 8,379 with schizophrenia were analyzed using a tree-based model. Results: The factor exerting the greatest influence on care time was "length of stay", so subjects were divided into 2 groups, a "short stay group" with length of stay ≦104 days, and "long stay group" ≧105 days. Each group was further subdivided according to dependence with regard to "activities of daily living", "psychomotor agitation", "verbal abuse", and "frequent demands/repetitive complaints", which were critical variables affecting care time. The mean care time was shorter in the long-stay group; however, in some long-stay patients, the mean care time was considerably longer than that in patients in the short-stay group. Conclusion: The results of this study suggest that it is necessary to construct a new payment system reflecting not only length of stay and nurse staffing levels, but also individual patient characteristics.
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