From people's preferences to political representation. The case of the Spanish regional elections

In this paper, we conduct an empirical analysis of the transition from voters' preferences to electoral outcomes, a process significantly influenced by the electoral system. We introduce a measure called 'support' that summarizes voters’ preferences. Then, we examine how these preferences are compressed under the plurality voting mechanism, which forces to select just one option. This choice is captured by the 'affinity', which singles out the preferred party for each voter. The final decision, though, is affected by strategic considerations and several other factors. Using survey data from three Spanish regions (Andalusia, Madrid, and the Valencian Community) prior to their respective Regional Elections, our findings indicate that political representation in all three Regional Parliaments would be more diverse if based on voters’ complete preferences (i.e., support). In all instances, smaller parties lose ground, a trend that emerges even before strategic considerations. These results suggest that the electoral system may exacerbate political polarization, diverging from social preferences.