Agree without aggregating: An extension of multi-criteria decision theory for multiple decision makers in the management of coastal erosion

Abstract

Coastal management is an example of a complex decision problem, where the outcome of and the managerial process itself is associated with a multitude of different impacts. One way to approach these kinds of situations is through the application of structured decision analysis. In addition to ensuring that existing knowledge is incorporated, structured decision analysis increases the transparency within the project. This paper examines to what extent multi-criteria decision analysis (MCDA) can be used to identify the need for negotiations to reach agreement in the management of coastal erosion involving multiple decision makers. MCDA is a tool to assess performance of management alternatives that help decision makers to identify the best available options from a number of predefined decision alternatives. As of today, MCDA takes into account the values from one decision maker. This creates a problem when dealing with multiple decision makers who may value the criteria differently. In this study, MCDA is expanded into what we call a pluralistic MCDA, which can include multiple decision makers. First, we develop decision theory for the pluralistic MCDA. To help determine the space for negotiations, we compute each decision maker’s willingness to change and introduce a new decision rule that trade off the fraction of decision makers that agree to the required overall willingness to change. Second, the pluralistic MCDA is applied on a coastal management problem in southern Sweden. For this, a comprehensive literature review was performed to identify standard practices and mitigation strategies used in coastal management with regards to coastal erosion. Next, a set of criteria was identified, combined with a set of unique rating scales. The potential of assessing different coastal erosion mitigation strategies using an extended version of multi-criteria decision analysis was then tested, first through simulations and then through a case study. The initial findings of this study indicate that pluralistic MCDA could provide coastal managers engaged in situations involving multiple decision makers with an efficient tool, when assessing management alternatives. In addition, pluralistic MCDA could provide a useful tool to increase the transparency and validity of the decision process.