Introduction

Making decisions between alternative investments, projects, or policies that affect the provision of ecosystem services often involves weighing up and comparing multiple costs and benefits that are measured in different metrics and are incurred at different points in time. For example, the establishment of a new protected area might involve costs in terms of the purchase of land, compensation of local communities, and ongoing maintenance and enforcement costs; and benefits in terms of biodiversity conservation, recreational use, and improved watershed services. These costs and benefits are likely to be measured in different units, incurred by different groups and have different time profiles. Organizing, comparing, and aggregating information on such a complexity of impacts, and subsequently choosing between alternative options with different impact profiles require a structured approach. Methods for evaluation or appraisal of complex decision contexts provide systems for structuring the information and factors that are relevant to a decision.

Benjamin Franklin’s description of his own approach to making complex decisions sets out the intuition behind evaluation methods (Franklin, 1772):