Finding an overall ranking of a group of products from rankings over multiple salient attributes is a problem of considerable interest. Assume an individual is faced with ranking m products or choice items. Assume the individual has n attributes, which s/he is using to describe the products, and has, for each attribute, an ordinal preference function ranking the choice items over that attribute. In other words, s/he has n rankings, each corresponding to an attribute. The problem of overall ranking involves combining these n rankings in some rational manner to form an overall preference ranking. This problem is analogous to a multi-objective decision problem in which the attributes constitute the objectives and the choice items are the alternatives. The problem is also analogous to the selection of a social welfare function from individual welfare functions. In this case, the attributes would correspond to the individuals in the society, and the choice items would correspond to the various possible economic bundles. A considerable body of literature has been written on these problems (see Arrow 1951; Luce and Raiffa 1957). Of particular interest are some of the concepts concerning criteria for rationally combining the attribute rankings to form the overall ranking. The first concept of interest is Pareto optimality. Assume A and B are two choice items, and that B is ranked above A by every attribute. Pareto optimality requires that B be ranked above A in the overall ranking. The second concept is that of positive association between the individual orderings and the overall ordering. All else being equal, this requires that if Item A improves with respect to Item B on one attribute's ranking, then A's ranking with respect to B in the overall ranking will not decrease. In a sense, this requirement ensures that the overall ranking is determined by the individual rankings. The final concept of interest is indifference to irrevelant alternatives. Assume we have a set of choice items and a group of attribute preference orderings, and that this leads to an overall ranking in which A > B. Assume we add an additional choice item, and that the attribute rankings are only modified by the insertion of this new item at its appropriate place in the individual rankings. Then the criteria of indifference to irrelevant alternatives implies that A will still be higher than B in the new overall ranking.
Read full abstract