I got a question from Alex Roe about the reasons Italy has this electoral system. Here’s my answer:
I’ve written about the motives behind the electoral reform before: you can find the academic paper here.
The argument is as follows:
In 2005, the centre-right wanted to minimize its losses and to keep attention on the party rather than the individual candidates (who were generally quite poor).
Normally, if you want to do those things, you switch to a system of proportional representation. You get people to vote for party lists rather than individual candidates, and you allocate seats in proportion to party vote shares. That avoids the heavy electoral punishment that happens under single member district systems. Although Italy’s electoral system between 1993 and 2005 wasn’t a pure single member district system (it was a mixed member proportional system), it did have a single member district element.
Unfortunately, the centre-right also wanted to keep the bipolar pattern of competition. Alleanza Nazionale was terrified that a switch to a proportional system would leave it out in the cold on the right of the spectrum. So the solution was to graft a special “bonus” for the largest coalition. That gave an incentive to build big coalitions capable of including parties that were opinion outliers.
The original plan was to give that bonus to the largest coalition in the Camera, and the largest coalition in the Senate.
Unfortunately, that would have been unconstitutional, because in the Senate it would have meant ignoring the regions in order to allocate the bonus.
So that national bonus got broken down into lots of different regional systems.
It’s this last part — unintended, and unforeseen — which has made the system as complicated as it is today.
All the stuff about the thresholds is just about screwing people over if they decide to defect from big coalitions, and granting favours to those in the coalitions. There were some real micro-politics going on at the time it was drafted.