Abstract
Japan's tax and social security systems are designed based on the concept of a standard household. However, in reality, a variety of households have emerged. In the social security system especially, households are more important than individuals are. In this study, we estimate the future of Japan's population and households using an agent-based model (ABM), in which we set the initial values to represent Japan’s actual population and household composition with individuals as agents, and which incorporates life events such as aging / death, marriage, childbirth, divorce, and cohabitation. According to our analysis, the progress of population decline, the declining birthrate, and aging is serious, and it is necessary to design systems that promote efficient social security expenditures and self-help to prepare for retirement. Our household estimates show that the proportion of households with three, four, or more inhabitants decreased sharply, and the rate of single-person households progressed rapidly, with approximately 60% of all households becoming single-resident. Since the number of elderly single-person households (particularly female elderly single-person households) increased significantly, it is important to design a system that assumes that the social security system will have to serve single-person elderly households.
