The seat-share estimates given by SWG, which suggest that the centre-right would win 176 seats, seem slightly optimistic. They give more seats to the centre-right than they would win if we assume a uniform national swing of 5.15% and a 9:33 split between the radical left and the centre left. Here’s how I worked it out.

• Take the Senate vote share in 2006 between the centre-left and the centre-right (48.96% to 50.21%)
• Take the current poll shares of the combined centre-left and the centre-right (42% to 53%), and scale up to 100%, ignoring smaller parties. This gives you 44.1 to 55.65
• Calculate the uniform national swing: ((48.96-44.1) +(55.65-50.21))/2 = 5.15%
• Assume that the Sinistra Arcobaleno and the Partito Democratico split the vote in rough proportion to their current poll shares (9:33).
• Multiply the left’s vote in each region by the uniform national swing, and then by 9/(33+9) to get the Partito Democratico’s estimated 2008 vote share

Done this way, the Partito Democratico does best in Tuscany, winning 43.79% of the vote – but even there, it loses to the Casa delle Liberta` on 43.86% of the vote (the Arcobaleno wins 12.35%).

Thus, the centre-right wins all the premia in the seventeen regions, which nets it 165 seats.

Assume further that

• the two coalitions split Molise one seat each;
• that the centre-right wins two seats abroad, as it did in 2006
• that, in Trentino Alto-Adige, the SVP romps home in Merano and Bressanone, and that the Union holds on in Bolzano and Rovereto. The Casa wins in Trento and Pergine Valsugana, winning two seats.

Thus, the centre-right wins a total of 170 seats. This is less than the SWG estimate, but still a comfortable majority – and much more secure than estimates based on which regions have historically voted left. Given the swing away from the centre-left, and its internal divisions, the centre-right can now be forecasted to have handsome majorities in both chambers.