This article has two related objectives. Firstly, I shall discuss the logical, conceptual and empirical anomalies of the canonical interpretations, and, secondly, I propose an alternative interpretation for the index, which leaves the sociological bias behind in favor of an economic approach. As pointed out, the economic approach analyses party systems as an "electoral market" in which the degree of constraints (rules and resources) has significant weight in the dynamics of "supply" (available political parties and policies offered and implemented) and "demand" (individual voters, economic classes, ethnic, linguistic or religious grounds and all kinds of social cleavages), and electoral volatility reflects the evolutive movements of the political market.
