If the qualitative or quantitative approach is used to complete the matrix as shown in Table 2.5.1, information for this approach related to the environmental impacts can be based on impact prediction. This information is also needed for the approaches involving importance weighting and ranking, rating, or scaling. If the importance weighting approach is used, the assignment of importance weights to decision factors, or at least the arrangement of them in a rank ordering of importance, is critical. Table 2.5.2 lists some structured importance weighting or ranking techniques which can be used to achieve this step. These techniques have been used in numerous environmental decision-making projects. Brief descriptions of several techniques from Table 2.5.2 are illustrated. In addition to the structured techniques, less formal approaches, such as reliance on scoping, can be used as a basis for importance weighting.
Ranking techniques for importance weighting basically involve the rank ordering of decision factors in their rela-
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