ABSTRACT
In his review of notable planning disasters, Hall proposes two ways for avoiding future disasters: improve forecasting methods and refine evaluation criteria by explicitly ranking gains and losses in the near against distant future. The prospective evaluation helps judge which of the ways of acting is more worthwhile than others. Evaluation methods focus on costs or inputs e.g. in the case of threshold analysis, or on outputs or values as in the case of multicriteria analysis or on input as well as output e.g. in cost-benefit analysis. The use of desirable scenarios for evaluative purposes implies new methodological innovations both for scenario building and evaluation. The most important differences between conventional and exploratory evaluation are found with regard to knowledge. The knowledge contents of conventional evaluation are rigorous and data-based with a view, in ex ante evaluation, to compare alternative policy proposals.
