True indexes and rational habit formation

In this paper we discuss the construction of true indexes when tastes change endogenously. True indexes take the substitution possibilities of the consumer to a changing economic situation into account when equating the utility level of a particular period to the utility level attained in the base period through an appropriate change in income or the wage level. When tastes change endogenously, the current decision depends on the past history of consumption but, by the same token, the future path of consumption will depend on the current choice. In a true index, these intertemporal links of the current decision have to be taken into account. For a particular specification of the habit formation process, this is achieved by an appropriate transformation of prices and expenditures. A true intertemporal wage index is computed for the period 1946–1967 in the U.S. Because of increasing needs and intertemporal rationality, this index is roughly constant and equal to 1: real wages remained constant!