A Quasi-Natural Experiment on Electoral Rules and Political Representation

We combine roll call votes and referendum decisions on identically worded legislative proposals to identify the effect of electoral rules on the way Swiss Members of Parliament (MPs) represent their constituents’ preferences. We exploit the fact that MPs in both Houses of Parliament are elected in the same electoral districts (the cantons). Yet, in the Lower House, MPs are elected using a proportional rule, while in the Upper House they are elected employing a majoritarian rule. We find that electoral rules matter strongly for political representation. The voting patterns of MPs are in line with three theoretical predictions regarding the influence of electoral rules on representation of constituents’ preferences: 1) The probability that a proportional-elected MP accepts a legislative proposal closely follows the share of voters that accept the proposal in the referendum. 2) In contrast, majority-elected MPs only react to the share of voters accepting a proposal in the referendum for shares close to the 50% threshold. 3) The estimated probability that an Upper House MP votes “yes” as a function of the share of voters voting “yes” in the referendum has an S-shape form with an inflection point close to 50%.