Description:
<jats:p>This paper is concerned with the theoretical problems of devising indexes of quality change and with some of the practical problems of constructing such indexes from market data, relating these to the various attempts to construct such indexes in the past. The general conclusion is that, while quality is inherently ordinal, there are three different indexes which might be taken as “measures” of quality change. If changes are sufficiently small, the values of all three indexes will coincide and then, only, can we consider any one of them to be an unambiguous measure of the change.</jats:p>