Social Decision Schemes

Social decision scheme (SDS) theory provides a mathematical framework for predicting group choices from group member preferences. A social decision scheme is a representation of a decision process that yields predicted group decisions given the initial preferences of members. As an example, consider a committee of employees who must choose among three health insurance plans being considered by their employer. The committee is composed of four employees, and each has a preferred plan. The four members may agree or disagree, but the goal is to endorse collectively one plan. Combining such individual preferences to obtain a collective decision encompasses both voting rules and a social influence process. Voting or decision rules are explicit or implicit rules for determining the group choice based on members' final votes. Common rules are majority (the alternative with 50% + 1 votes wins), unanimity (the alternative with all votes wins), and plurality (the alternative with more votes than any other wins). In addition to using voting rules, small groups also typically discuss the decision options, and preferences change as a result of information exchange, persuasion, and social pressure. In the aforementioned example, assume that the committee adheres to a majority decision rule: Three of the four members must ultimately agree to adopt a particular health plan. Unless they begin with such a majority, they will likely discuss the health care plans, and the preferences that individuals bring to the group may change during this discussion. SDS theory captures how different alignments of initial preferences are channeled through voting and social influence processes to yield a collective choice.

The fundamental question in the SDS approach is, What is the committee likely to decide, given the initial preferences of its members or, more gener- [Page 771]ally, given the preferences of the people who are potential members of the committee? The four elements of SDS are (1) individual preferences, (2) group preference composition, (3) social decision schemes, and (4) group choices. This entry considers each of these.