ABSTRACT
A. Wald (1939) escaped from the then current insistence that the cost of living should be settled by a price index. When a utility function is given, it is possible to determine the relation between incomes that have the same purchasing power at different prices. Generally this could be any monotonic relation. Use of a price index requires it always to be a homogeneous linear relation, a line through the origin, for which the price index gives the slope.
