Measuring party system change : a systems perspective

The term "party system", explained Giovanni Sartori, refers to the pattern of interactions among major parties. That pattern can be represented as a type and treated as a proper unit of analysis. When "party system" is defined in this way, it becomes clear that the scholarship lacks a direct measure of "party system change". The Sartori approach to party system change is not the only legitimate way to understand this concept, but it does target an undoubtedly important feature of political systems - namely, the stability of major-party interactions. This article develops a new indicator, the index of fluidity, which measures the extent of such stability. Applying the index to Africa, we show there is significant cross-national variation in fluidity and weak correlation between fluidity and (Pedersen) volatility.