Aggregating multiple ordinal rankings in engineering design: the best model according to the Kendall’s coefficient of concordance

Aggregating the preferences of a group of experts is a recurring problem in several fields, including engineering design; in a nutshell, each expert formulates an ordinal ranking of a set of alternatives and the resulting rankings should be aggregated into a collective one. Many aggregation models have been proposed in the literature, showing strengths and weaknesses, in line with the implications of Arrow's impossibility theorem. Furthermore, the coherence of the collective ranking with respect to the expert rankings may change depending on: (i) the expert rankings themselves and (ii) the aggregation model adopted. This paper assesses this coherence for a variety of aggregation models, through a recent test based on the Kendall's coefficient of concordance (W), and studies the characteristics of those models that are most likely to achieve higher coherence. Interestingly, the so-called Borda count model often provides best coherence, with some exceptions in the case of collective rankings with ties. The description is supported by practical examples.

Weight Approximation for Spatial Outcomes

When preferences explicitly include a spatial component, it can be challenging to assign weights to geographic regions in a way that is both pragmatic and accurate. In multi-attribute decision making, weights reflect cardinal information about preferences that can be difficult to assess thoroughly in practice. Recognizing this challenge, researchers have developed several methods for using ordinal rankings to approximate sets of cardinal weights. However, when the set of weights reflects a set of geographic regions, the number of weights can be enormous, and it may be cognitively challenging for decision makers to provide even a coherent ordinal ranking. This is often the case in policy decisions with widespread impacts. This paper uses a simulation study for spatial preferences to evaluate the performance of several rank-based weight approximation methods, as well as several new methods based on assigning each region to a tier expressing the extent to which it should influence the evaluation of policy alternatives. The tier-based methods do not become more cognitively complex as the number of regions increases, they allow decision makers to express a wider range of preferences, and they are similar in accuracy to rank-based methods when the number of regions is large. The paper then demonstrates all of these approximation methods with preferences for water usage by census block in a United States county.

Wellbeing measures of mortality risks: life-cycle contradictions and ordinal index challenges

The value of a statistical life (VSL) monetizes the expected loss in wellbeing associated with the risk of death. The utility loss resulting from a fatality is central to the empirical framework for estimating the VSL. The VSL trajectory over the life cycle exhibits an inverted-U shape, following a trajectory similar to that of lifetime patterns of consumption. The U-shaped pattern displayed by happiness measures over the life cycle is the opposite of the inverted-U shape pattern displayed by the VSL. It is consequently inappropriate to use happiness measures as ordinal ranking substitutes for the VSL for the purposes of estimating the benefits of mortality risk reduction. Compared to ordinal wellbeing scales, the VSL also offers a variety of additional capabilities by providing a cardinal index of the unit benefits for changes in mortality risks.

Modelling the Impacts of Aquaculture in Wetland Ecosystems for Sustainable Aquaculture Management: An Integrated Ecosystem Approach

This research integrates information from both environmental and social sciences to inform effective management of the wetlands. A three-stage research framework was developed for modelling the drivers and pressures imposed on the wetlands and their impacts to the ecosystem and the local communities. Firstly, a Bayesian Belief Network (BBN) was used to predict the probability of anthropogenic activities affecting the delivery of different key wetland ecosystem services under different management scenarios. Secondly, Choice Experiment (CE) was used to quantify the relative preferences which key wetland stakeholder group (aquaculturists) held for delivery of different levels of these key ecosystem services. Thirdly, a Multi-Criteria Decision Analysis (MCDA) was applied to produce an ordinal ranking of the alternative management scenarios accounting for their impacts upon ecosystem service delivery as perceived through the preferences of the aquaculturists. This integrated ecosystem management approach was applied to a wetland ecosystem in Setiu, Terengganu, Malaysia which currently supports a significant level of aquaculture activities. This research has produced clear guidelines to inform policy makers considering alternative wetland management scenarios: Intensive Aquaculture, Conservation or Ecotourism, in addition to the Status Quo. The findings of this research are as follows. The BBN revealed that current aquaculture activity is likely to have significant impacts on water column nutrient enrichment, but trivial impacts on caged fish biomass, especially under the Intensive Aquaculture scenario. Secondly, the best fitting CE models identified several stakeholder sub-groups for aquaculturists, each with distinct sets of preferences for the delivery of key ecosystem services. Thirdly the MCDA identified Conservation as the most desirable scenario overall based on ordinal ranking in the eyes of most of the stakeholder sub-groups. Ecotourism and Status Quo scenarios were the next most preferred and Intensive Aquaculture was the least desirable scenario. The methodologies developed through this research provide an opportunity for improving planning and decision making processes that aim to deliver sustainable management of wetland ecosystems in Malaysia.

On linear wine score aggregators and the preservation of group preferences

Purpose This paper aims to identify the potential conflicts that arise between the actual and the revealed preference of a panel of wine judges when the panel’s evaluation is derived by a linear aggregation of individual scores. Design/methodology/approach A standard axiomatic social choice theoretical model is used to derive and examine the findings. Findings The findings show that even with the application of a simple majority rule over the pairwise ranking of wines, preferences may be misrepresented by the ordinal ranking of the wine score aggregation. Originality/value A number of wine competitions and reviews, to date, use some form of linear aggregation to represent group preferences. Furthermore, tests surrounding wine judge performance are largely dependent on some underlying true measures usually derived from a linear aggregation. The results imply that care should be taken in these regards.