Elections with partially ordered preferences

Suppose an organization has a committee with multiple seats, and the committee members are to be elected by a group of voters. For the organization, the possible alternatives are the possible sets of individuals who could serve together. A common approach is to choose from among these alternatives by having each voter cast separate votes on the candidates for each seat. When this type of ballot is used, important characteristics of the set of individuals on the committee (such as what percentage of the members will be female) might not be explicitly considered by the voters. Another approach that has been used is to have each voter cast a ballot which ranks all possible sets of members. However, this approach can require the voters to weigh a relatively large number of alternatives. This paper considers group decisions where it is desirable to: (1) explicitly consider characteristics of alternatives and (2) have a relatively small number of options upon which a voter has to express his preferences. The approach that we propose has two steps: First voters vote directly on pertinent characteristics of alternatives; Then these votes are used to indirectly specify preferences on alternatives. The indirectly specified preferences are ones that are naturally modeled using partially ordered sets. We identify some specific methods that could be applied in the second step. In addition, by replacing the indirectly specified preferences in a suitable way, we suggest a technique that can use any positional, pairwise, or other voting method that accepts totally (or "completely") ordered inputs to tally ballots. We also describe another way to potentially compute pairwise rankings from partially ordered alternatives and discuss some practical and theoretical difficulties associated with our approach.