If a particular good or service is defined in terms of scientifically measurable quantities, then measurement difficulties involving quality changes could sometimes be avoided. For example, Nordhaus (1994) examined "lighting," in which he defined quantities of light in lumens, the same measurement employed by physicists studying light flow. He found that, because of scientific and engineering advances in lighting technology and in energy generation and transmission, the amount of human labor needed to produce light throughout history has gone down dramatically. In particular, the amount of light that, in 1800, required 5.4 hours of total labor for all aspects of production, required only 0.22 hours in 1900, 0.00060 hours in 1990, and 0.00012 hours in 1992. Nordhaus does not associate these achievements with the R&D expenditures that made them possible. Nonetheless, he demonstrates that, in terms of basic, physical definitions of progress (such as lumens produced per hour of human labor), the benefits of scientific advancement can be quite large and tend to be much larger than what is often revealed by traditional, economic measures of change.

5 Because his study focused on price-indexing, Siegel does not offer an explanation for why these percentages across time were different. A simple explanation does not exist, although the circumstantial, individual successes of a small number of new products might provide a partial explanation.

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