Introduction

Leontief's original input–output framework (Leontief, 1936) conceived of industry production functions, which he frequently referred to as production “recipes,” as measured in physical units, such as specifying the technical coefficients in tons of coal or bushels of wheat, as inputs, required per dollar's worth of an industry's output or per ton of steel output. However, the data collection requirements and a number of other constraints rendered implementation of the framework in physical units too unwieldy, certainly at the time and even today to a lesser extent. Hence, the basic methodology for input–output analysis evolved, in both theory and application, through measuring all quantities in value terms with implicit fixed prices, as detailed in earlier chapters. Even late in his life, however, Professor Leontief continued to explore ways in which the framework could be implemented more widely in physical units rather than value terms (Leontief, 1989). A number of researchers, such as Duchin (1992), carried on with that work and continued to develop it.

The contributions of many researchers have extended the input–output framework incrementally in the direction of employing physical units and, in the process, have helped lay the groundwork for new research areas such as industrial ecology and ecological economics, which are topics addressed in more detail in Chapter 10. In addition, there have been substantial developments in related areas where public policy concerns have encouraged such development and data have been collected to help implement the framework.