Choice via Grouping Procedures

In this paper, we consider a natural procedure of decision-making, called a “Grouping Choice Method”, which leads to a kind of bounded rational choices. In this procedure a decision-maker (DM) first divides the set of available alternatives into some groups and in each group she chooses the best element (winner) for her preference relation. Then, among the winners in the first round, she selects the best one as her final choice. We characterize Grouping Choice Methods in three different ways. First, we show that a choice function is a Grouping Choice Method if and only if it is a Rational Shortlist Method (Manzini and Mariotti, 2007) in which the first rationale is transitive. Second, Grouping Choice Methods are axiomatically characterized by means of a new axiom called Elimination, in addition to two well-known axioms, Expansion and Weak WARP (Manzini and Mariotti, 2007). Third, Grouping Choice Methods are also characterized by a weak version of Path Independence.