When the Prodi government fell, I posted a note explaining how the government’s duration could have been predicted by models from political science. I thought I would do the same for the Berlusconi government now that we know the seat distribution in the Senate.

The model [King et al. 1990] depends on seven variables. The two which have changed since Prodi are party system fractionalization and polarization. They’re calculated as follows:

• Fractionalization in the Senate: [Rae index] take the sum of squares of each party’s share of seats, subtract it from 1, and multiple by 1000 to get a nice number: 633.1, in this case.
• Polarization: [according to Powell 1982] take the summed vote share of each ‘extremist’ party in the Senate elections: Lega Nord, Sinistra Arcobaleno, La Destra, Sinistra Critica, Pcl, Grilli Parlanti = 14.9%

The model predicts a mean duration of 37 months, with a standard deviation of 5 and a half months. So, if the model is roughly correct, we can be 95% certain that the Berlusconi government will fall between December 2010 and January 2012. This, of course, does not mean that Berlusconi will exit from the scene during these dates, but that the composition of the government will change, and Berlusconi may be formally re-invested in the same way he was in 2005, when a poor performance in the regional elections caused his resignation and re-appointment.