Assumptions regarding the aggregation of time stream data (e.g. "discounting") are crucial in the evaluation of regional development proposals and the assessment of environmental impacts. Nonetheless, present practice reflects a great deal of confusion, ambiguity, caprice, and downright error in the calculation and implementation of such assumptions. We present in this paper the outlines of an approach to inter-temporal indicator evaluation for use in the analysis of regional development alternatives. Our ultimate objective is pragmatic: We wish to develop a practical framework for the reduction and comparison of time stream data for evaluation of public programs and policies. As a foundation for this approach, however, it has been necessary critically to review the existing controversy on intertemporal aggregation in a public policy context, and to clarify the practical implications of the, points at issue. Three interrelated themes pervade this review and provide a conceptual focus for the work
