the alternative methods available and the selection of a particular one depends on the methods’ accuracy in representing responses to regulatory incentives and constraints, their sensitivity to the particular regulatory changes being assessed, and their ability to accurately estimate the outcomes of interest in the assessment.

Different indicators can be used to assess magnitudes and trends in pollution prevention and control, energy efficiency, emissions, air quality, and health effects (e.g., NRC 1999; Esty 2001; Hayward 2004). Table 5-1 lists possible indicators for each. Many of these indicators vary over time and space or from plant to plant, and some degree of averaging or smoothing may need to be done before the data can be analyzed. In many cases, the data currently are not available from a single comprehensive source (or even distributed among many sources), and thus incomplete data would be used for drawing inferences. Furthermore, the list of measures in Table 5-1 includes factors that are quantitative and directly indicative of the targeted outcome, such as the emissions from individual plants, industries, and states, as well as other factors that are more qualitative and difficult to measure, such as the rate of innovation for pollution prevention and control technology.

Because many of the outcomes and indicators in Table 5-1 are affected by a number of factors beyond the realm of the NSR rules (or even pollution control laws in general), such as economic conditions, government investment in research and development (R&D), fuel supplies and prices, and meteorological conditions, these other factors and data should also be considered in analyses that attempt to assess the likely impact of NSR rule changes on the outcomes of interest. Thus, any assessment involves (explicitly or implicitly) comparing two different estimates: an estimate of what would have happened had the rule changes not occurred and an estimate of what will happen with the rule changes. Both are subject to substantial uncertainty, and, as discussed in Chapter 6, it will be necessary to consider a range of possible scenarios for the economic and environmental assumptions that are applied to estimate and compare outcomes of the revised NSR rules with outcomes of the NSR rules before the revisions.

The remainder of this chapter reviews the major approaches and methods that have been, or might be, used to assess the impacts of changes in the NSR rules on the outcomes in Table 5-1 at the level of the firm, the industrial sector, and the economy. The committee considered it important to review the full range of methods available for this purpose to determine the extent to which the different approaches could assist in responding to the committee’s charge. This survey is deliberately broad



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