From Duverger to the Seat Product: Seeking a Pattern in Experts’ Evaluation of Electoral Systems

Widely influential Duverger’s “law” and “hypothesis” describe the main direction of influence of electoral rules on party systems, however, their formulations are quite blurry what makes their application to concrete electoral results often ambiguous. Therefore, this research conducted an original survey among electoral experts (n=131) to explore whether they apply Duverger’s rule in a consistent pattern which could lead to its less ambiguous specification. Experts’ responses revealed a considerable heterogeneity which indicates that their evaluation of electoral systems is not driven by an unambiguous theoretical framework. Nevertheless, experts were on average consistent with the quantification of the Duverger’s rule done by Taagepera (2007) in Seat Product Models which served as benchmarks for this study. Therefore, this research concludes that the Seat Product Models constitute a suitable specification of the Duverger’s logic which should be used as a baseline in electoral studies. The reason is that the Models allow more fine-grained evaluation of electoral systems, while being already consistent with experts’ perception of electoral system effects.

极具影响力的迪韦尔热（Duverger）‘定律’与‘假说’系统阐述了选举规则对政党体系的主要影响方向，但其原始表述相当模糊，这使得将其应用于具体选举结果时往往存在歧义。为此，本研究针对选举专家开展了一项原创性调研（样本量n=131），旨在探究专家们是否以一致的模式应用迪韦尔热定律，进而推动该理论实现更清晰的界定。调研结果显示，专家的判断存在显著异质性，表明他们对选举制度的评价并未依托明确统一的理论框架。不过，从平均水平来看，专家们的判断与本研究的基准参考——塔杰佩拉（Taagepera）2007年提出的席位乘积模型（Seat Product Models）中对迪韦尔热定律的量化方式相符。因此，本研究得出结论：席位乘积模型恰当地界定了迪韦尔热的理论逻辑，可作为选举研究的基准框架；其优势在于，该模型不仅能够对选举制度开展更为精细化的评价，同时也契合专家们对选举制度效应的普遍认知。