Valuation of ecosystem services and social choice: the impact of deliberation in the context of two different aggregation rules

Abstract

This paper describes an empiric study of aggregation and deliberation—used during citizens’ workshops—for the elicitation of collective preferences over 20 different ecosystem services (ESs) delivered by the Palavas coastal lagoons located on the shore of the Mediterranean Sea close to Montpellier (S. France). The impact of deliberation is apprehended by comparing the collectives preferences constructed with and without deliberation. The same aggregation rules were used before and after deliberation. We compared two different aggregation methods, i.e. Rapid Ecosystem Services Participatory Appraisal (RESPA) and Majority Judgement (MJ). RESPA had been specifically tested for ESs, while MJ evaluates the merit of each item, an ES in our case, in a predefined ordinal scale of judgment. The impact of deliberation was strongest for the RESPA method. This new information acquired from application of social choice theory is particularly useful for ecological economics studying ES, and more practically for the development of deliberative approaches for public policies.

Appendix

1.1 Appendix 1

The list of the ecosystem services used in the study (Table 6).

Table 6 The set of the twenty ecosystem services (ESs) used in this study

1.2 Appendix 2

Box B: Formulation of the majority judgement method

Consider a set of a finite number of ecosystem services $S=\{{SE}_{1}, \dots , {SE}_{m}\}$; a finite number of voters $V=\{1, \dots , n\}$; and a common language of grades $\Lambda =\{\alpha , \beta , \gamma , \dots \}$ which is a totally ordered set. The grades or words are “absolute” (Balinski and Laraki 2014) in the sense that every voter uses them to measure the level of priority of each ES independently

The matrix of inputs is formulated as:

$$\varphi =\left[{\alpha }_{11} \cdots {\alpha }_{1m} \vdots \ddots \vdots {\alpha }_{n1} \cdots {\alpha }_{nm}\right]$$

Where ${\alpha }_{ij}=\varphi ({ES}_{i}, v)\in \Lambda$ is the grade assigned by voter $v\in V$ to ${ES}_{i}\in S$

The majority grade attributed to an ES by all the voters correspond to its middlemost or median grade when $n$ is odd and its lower middlemost when $n$ is even (Balinski and Laraki 2014)

Suppose an ES majority grade is ${\alpha }^{*}$, and that $p\%$ of his grades are higher than ${\alpha }^{*}$ and $q\%$ are lower. Then its majority gauge is $(p,{\alpha }^{*}, q)$, where $p>q$ implies ${\alpha }^{*}$ is endowed with a “+”, and otherwise it is endowed with a “−” (Balinski and Laraki 2010, 2014). It is formulated as follow:

$${\alpha }^{*}=\left\{{\alpha }^{+} \,\,if\,\, p>q, {\alpha }^{-}\,\, if\,\, p< q\,\, \text{and} \,\,a^{\circ } \,\,if\,\, p = q\right\}$$

The majority gauge $(p,{\alpha }^{*}, q)$ determine the majority-gauge-ranking of ESs

Consider two ESs ${ES}_{1}$ and ${ES}_{2}$ with majority gauges $(p,{\alpha }^{*}, q)$ and $(r,{\beta }^{*}, s)$, respectively. The majority-gauge-ranking “${\succ }_{mg}$” places ${ES}_{1}$ ahead of ${ES}_{2}$, ${ES}_{1}{\succ }_{mg}{ES}_{2}$, or $(p,{\alpha }^{*}, q)$ ahead of $(r,{\beta }^{*}, s)$, $(p,{\alpha }^{*}, q){\succ }_{mg}(r,{\beta }^{*}, s)$ when:

• ${\alpha }^{*}\succ {\beta }^{*}$, or

• ${\alpha }^{*}={\beta }^{*}={\alpha }^{+}$and $p>r$, or

• ${\alpha }^{*}={\beta }^{*}={\alpha }^{^\circ }$ and $p>r$

• ${\alpha }^{*}={\beta }^{*}={\alpha }^{-}$ and $q<s$