We usually find a considerable degree of correlation between indicators and also between different sets of weights that we should ever think of using. Consequently we are likely to find that alternative index numbers using different weights show similar and often approximately proportionate movements. That this is so in most economic applications is due to the nature of the actual world and not simply to the formal characteristics of index number techniques.

p. 7; As cited in: Chao, Hsiang-Ke. Representation and structure: The methodology of econometric models of consumption. 2002. - The Role of Measurement in Economics. 1951