Evaluation and Decision Support Tools (chapter 7)

7.1 Introduction Making decisions between alternative investments, projects or policies that affect the pro-vision 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 on-going maintenance and en-forcement costs; and benefits in terms of biodiversity conservation, recreational use and improved watershed services. These costs and benefits are likely to be measured in differ-ent units, incurred by different groups and have different time profiles. Organising, compar-ing and aggregating information on such a complexity of impacts; and subsequently choos-ing between alternative options with different impact profiles requires a structured ap-proach. 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): 'When difficult cases occur, they are difficult chiefly because while we have them under consideration, all the reasons pro and con are not present to the mind at the same time … To get over this, my way is to divide half a sheet of paper by a line into two columns; writing over the one " Pro " , and the other " Con " . Then … I put down under the different heads short hints of the different motives … for and against the measure … I endeavour to estimate their respective weights; where I find one on each side that seem equal, I strike them both out. If I find a reason pro equal to two reasons con, I strike out three … and thus proceeding I find at length where the balance lies … And, though the weight of reasons cannot be taken with the precision of algebraic quantities, yet when each is thus considered, separately and comparatively, and the whole lies before me, I think I can judge better, and am less liable to take a rash step.' There are a number of decision support tools available to help decision makers to structure the information and factors that are relevant to a decision and to select between