These index numbers are at best rather crude and inaccurate illustrations of changes which have occurred. In periods of slow alterations in the relation between the supply of and the demand for money they do not convey any information at all. In periods of inflation and consequently of sharp price changes they provide a rough image of events which every individual experiences in his daily life. She has little use for computations disregarding changes both in quality and in the amount of goods which she is able or permitted to buy at the prices entering into the computation. In practical life nobody lets himself be fooled by index numbers.
Nobody agrees with the fiction that they are to be considered as measurements.
Where quantities are measured, all further doubts and disagreements concerning their dimensions cease. These questions are settled. Nobody ventures to argue with the meteorologists about their measurements of temperature, humidity, atmospheric pressure, and other meteorological data. But on the other hand nobody acquiesces in an index number if he does not expect a personal advantage from its acknowledgment by public opinion. Human action originates change.