Plurality, Proportionality, Governability and Factions

Common sense suggests that majoritarian parliaments produce more efficient governments than proportional ones, because fewer decision-makers are involved. Empirical evidence offers only limited support for this claim. A possible explanation is that the true decision-makers are not actually the parties, but rather the factions within them. We consider some stylised real proportional cases, i.e. Germany, Italy and the Netherlands, and use simulation to assess the weight that factions must have for governability to be lower in first-past-the-post than in threshold proportionality. Overall, our results provide support for the hypothesis suggested.