Comparing group deliberation to other forms of preference aggregation in valuing ecosystem services

Mackenzie B Murphy, Dartmouth College, Hanover, NH
Georgia Mavrommati, School for the Environment, University of Massachusetts, Boston, MA
Varun Rao Mallampalli, Department of Civil and Environmental Engineering, Duke University, Durham, NC
Richard B Howarth, Environmental Studies Program, Dartmouth College, Hanover, NH
Mark E Borsuk, Department of Civil and Environmental Engineering, Duke University, Durham, NC

DOI: http://dx.doi.org/10.5751/ES-09519-220417

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Abstract

Deliberative methods for valuing ecosystem services are hypothesized to yield group preferences that differ systematically from those that would be obtained through calculative aggregation of the preferences of participating individuals. We tested this hypothesis by comparing the group consensus results of structured deliberations against a variety of aggregation methods applied to individual participant preferences that were elicited both before and after the deliberations. Participants were also asked about their perceptions of the deliberative process, which we used to assess their ability to detect preference changes and identify the causes of any changes. For five of the seven groups tested, the group consensus results could not have been predicted from individual predeliberation preferences using any of the aggregation rules. However, individual postdeliberation preferences could be used to reconstruct the group preferences using consensual and rank-based aggregation rules. These results imply that the preferences of participants changed over the course of the deliberation and that the group preferences reflected a broad consensus on overall rankings rather than simply the pairwise preferences of the majority. Changes in individual preferences seem to have gone largely unnoticed by participants, as most stated that they did not believe their preferences had substantially changed. Most participants were satisfied with the outcome of the deliberation, and their degree of satisfaction was correlated with the feeling that their opinion was heard and that they had an influence on the outcome. Based on our results, group deliberation shows promise as a means of generating ecosystem service valuations that reflect a consensus opinion rather than simply a collection of personal preferences.

Key words

deliberative multicriteria evaluation; participatory methods; shared values; trade-off weights; value formation

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