Trading Oversized Parliaments for Proportionality - Or Vice Versa? A Comparative Analysis of Mixed-Member Proportional Systems in the German Länder

The German-type mixed-member proportional (MMP) system is considered a model for electoral reform worldwide. But even this system type has its own drawbacks and pitfalls, as recent evidence shows. Since the 1990s the MMP system for the German Bundestag continuously produced surplus seats which critically affected the proportionality among parliamentary parties. Eventually the German election law was changed in 2013, now providing for a full compensation of surplus seats. However, it soon became clear that the new electoral system realized perfect intra-parliament proportionality only in exchange for heavily oversized parliaments when the 2017 election led to an "inflated Bundestag" with more than 100 additional seats. This outcome triggered a debate about a further reform of the Bundestag MMP system that may curb parliamentary size without compromising intra-parliamentary proportionality. Quite surprisingly, the German Länder have never been addressed in this respect. Most of them have not only employed MMP systems for several decades but also established legal regulations that provide for a partial or full compensation of surplus seats respectively. In other words, the Länder form a "natural laboratory" in which the trade-off between proportionality and parliamentary size that is a general characteristic of MMP systems can be explored comparatively. Our paper does so by first elaborating on the theoretical mechanisms between institutional features of MMP systems on the one hand and intra-parliamentary proportionality and parliamentary size on the other. Relevant hypotheses are then examined all MMP elections in the Länder between 1946 and 2017. Based on these findings, we finally reflect on the implications for the German context as well as for the understanding of MMP systems in general.