Majority, proportionality, governability and factions

Commonsense wisdom claims that majoritarian parliaments produce more efficient governments than proportional ones, because there are less decisors involved. Empirical evidence gives poor support to this claim. A possible explanation is that the real decisors may be not the parties, but the factions within them. We (a) assumed as factions of parties in system i the parties that provide the same government coalition in pure proportionality, (b) considered some stylized real cases, i.e. Germany, The Netherlands and Italy and (c) looked through simulation for a weight of factions such that governability is lower in FPTP than in threshold proportionality. In one case (The Netherlands) this can occur only under peculiar circumstances; in another one (Italy) it occurs for a high role of the factions, and in the last one it occurs also for a low role of the factions. Overall, our results provide support for the suggested hypothesis.