多期間CPI,貯蓄デフレータおよび貯蓄減価率

抄録

Savings are said to reduce their value under hyper-inflation in daily conversation. Economic Planning Agency and Zensen-Domei propose different deflators for savings and different formulas for the rate of value reduction in savings. These two methods lack theoretical reasoning. This paper defines an intertemporal and an atemporal consumer price index, following Pollak, and points out the followings. The intertemporal CPI is the suitable deflator for assets such as savings, whereas the theoretical concept of the official CPI is atemporal. The ratio of the intertemporal to atemporal CPI depends on the expected rate of inflation and the interest rate. The atemporal CPI underestimates the intertemporal CPI under hyper-inflation or low interest rate. The rate of value reduction in savings is defined and is related to the savings' deflator. The problems involved in the Economic Planning Agency and the Zensen-Domei methods are pointed out.