Many studies exploit close elections in a regression discontinuity framework to identify partisan effects, that is, the effect of having a given party in office on some outcome. We argue that, when conducted on single-member districts, such design may identify a compound effect: the partisan effect, plus the majority status effect, that is, the effect of being represented by a member of the legislative majority. We provide a simple strategy to disentangle the two, and test it with simulations. Finally, we show the empirical relevance of this issue using real data.

This study addresses the question of why so many of the world's legislators are lawyers or law graduates. Drawing from previous studies on lawyer-legislators and electoral systems, it develops the argument that ‘first-pass-the-post’ single-member district electoral systems presume a principal-agent logic of representation and are therefore conducive to political parties selecting representatives with either occupational experience or educational training in the field of law. By contrast, proportional representation (PR) elections presume a microcosm model of representation incentivizing parties to select candidates representing diverse demographic and occupational backgrounds. This conjecture is tested by examining legislator backgrounds in three large parliaments with mixed electoral systems: Germany, Japan, and South Korea. As expected, single-member plurality elections are linked to a greater share of lawyers and law graduates in parliaments compared to those elected via PR even after controlling for several alternative explanations.