Evaluating the impacts along any one of these dimensions is hard enough. For example,
judging alternative instruments in terms of cost-effectiveness alone is difficult, since a comprehensive
assessment of cost would include not only the negative impacts on the regulated
entity but also monitoring and enforcement costs and general equilibrium impacts outside
the sector targeted for regulation. Considering several dimensions is harder still. Beyond
the theoretical and empirical challenges involved, there is a sobering conceptual reality: the
absence of an objective procedure for deciding how much weight to give to the competing
normative criteria. As a result, selecting the “best” instrument involves art as well as science.