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The centre-right government of Silvio Berlusconi, Italy’s prime minister, pushed through major changes to the electoral system in a law passed in December 2005.
It abolishes the system, used since 1994, in which 75 per cent of parliamentary seats were decided in British-style, first-past-the-post constituency contests, and 25 per cent were allocated by proportional representation.
In its place, it restores the system of full proportional representation used until the national elections of 1994.
The precise impact of the new system on the April 9-10 vote is hard to predict.
Some experts say Mr Berlusconi ordered the change because he feared defeat at the hands of the centre-left opposition and was determined to minimise his losses.
Others say the new system may benefit the centre-right more than the centre-left, because it will tend to favour the coalition that is more internally united and made up of larger political parties.
Some politicians are concerned that the new system will produce a split parliament, with one coalition gaining a majority in one chamber and another coalition taking control of the other one. This would paralyse effective government, they fear.
All experts agree that, under the new system, the winning coalition needs to be as broad as possible - which explains why both Mr Berlusconi and Romano Prodi, his centre-left challenger, are bidding for the support of small, fringe parties that may command as little as 0.5 per cent of the vote.
Here are the main rules of the new electoral system:
CHAMBER OF DEPUTIES (lower house of parliament)
A party linked to a coalition needs to win at least 2 per cent of the vote to win a seat.
A party running on its own needs at least 4 per cent.
A coalition of parties needs at least 10 per cent.
The winning coalition is guaranteed at least 340 seats in the 630-seat chamber, however narrow its margin of victory.
SENATE (upper house)
A party linked to a coalition needs at least 3 per cent of the vote to win a seat.
A party running on its own needs at least 8 per cent.
A coalition of parties needs at least 20 per cent.
Seats are distributed on a regional basis, and the winner in each region will be given at least 55 per cent of the region’s seats.
THE CURRENT BALANCE OF POWER
Berlusconi’s ruling centre-right coalition occupies 325 of the Chamber of Deputies’ 610 seats and 167 of the Senate’s 320 seats.