Aspects of Power Overlooked by Power Indices

The a priori voting power indices concentrate on actor resource distributions and decision rules to determine the potential influence over outcomes by various actors. That these indices sometimes seem to be at odds with the intuitive distribution of real power in voting bodies follows naturally from their a priori nature. Indices based on actor preferences address this by equating an actor’s voting power with the proximity of voting outcomes to his/her ideal point. It is, however, shown that in some cases the preference-based indices are just as questionable as the classic ones. The main aim of this paper is to delineate the proper scope of power indices. In the pursuit of this aim we try to show that the procedures resorted to in making collective decisions are as important—if not more so—as the actor resource distribution. We review some results on agenda-systems to drive home this point. The proper role of power indices then turns out to be in the study of actor influences over outcomes when the actors are on the same level of aggregation (individuals, groups, states) and “comparable” in the sense of having similar sets of strategies at their disposal and preferences are not taken into consideration, e.g. because a veil of ignorance applies.