The forthcoming article “Turnout Across Democracies” by Helios Herrera, Massimo Morelli, and Salvatore Nunnari is summarized here:
Electoral participation varies a lot across democracies. While the previous literature has focused exclusively on the electoral system, we show that the institutional mapping from seats in parliament to the power of changing policies matters at least as much. Even when the electoral system is one of the two pure extremes (winner-take-all or PR), other institutions affect the degree of proportionality of power shares. Such institutions include the veto power of a qualified minority, the way margins of victory translate into committee assignments or guarantee a more powerful mandate, the division of powers between the legislature and the executive, federalism, the power to appoint constitutional judges, etc.
We show that, for any distribution of voters’ preferences, turnout is highest for intermediate levels of the overall institutional mapping from votes to power. The degree of power sharing which maximizes turnout is closer to even power sharing when electoral competition is lower, and closer to winner-take-all when electoral competitiveness is higher. The intuition is as follows. As we move a away from an even power sharing system, the institutional system becomes more and more similar to a system where power is concentrated in the hands of the party that obtains a plurality of the votes. Hence, turnout drops for any lopsided preference distribution because the underdog side has no chance of obtaining the plurality of the votes, which is all that matters in this case. A system with even power sharing will typically display moderate turnout for all preference distributions, as the incentives to turnout remain even in a very lopsided election: there is always a possible power gain for turning out more. Finally and crucially, for intermediate systems, i.e. between full power sharing and no power sharing, turnout is the highest. It is particularly striking that this theoretical finding holds with all the well known theories of turnout, from instrumental voting to ethical voting and voters’ mobilization.
The important message for future empirical researchers is that any prediction on how turnout depends on the proportionality of the whole political system can be tested using the proportionality indices for the electoral rules, as was done so far in the literature, only if the researcher restricts the sample of countries to those with similar mappings from seats to power, for instance countries with similar division of power between the legislature and the executive. Similarly, the role of the degree of power to the legislature must be evaluated only while keeping the electoral rule constant. For example, we find that turnout increases significantly more with competitiveness in FPTP systems with respect to PR systems when keeping important components of the mapping from seats to power constant.