Rome, November 16 - An opinion poll released Friday by the SWG statistics institute on behalf of Italian state broadcaster RAI showed that the main centre-left Democratic Party (PD) remains the favorite for the next parliamentary elections, having gained 0.2% since last week. The second biggest group, comedian Beppe Grillo's anti-establishment Five Star Movement (M5S), lost 0.5% in the polls, while the anti-graft Italy of Values (IdV) party also dropped 0.5% following the arrest of the former caucus head in Lazio on Tuesday. Ex-premier Silvio Berlusconi's People of Freedom (PdL) party gained 0.3% in the polls. The survey was conducted by phone and email November 12-15, said the statistics institute. Those surveyed said that they did not believe that the center-left PD would reach the necessary percentage to have a ruling majority outlined by the proposed electoral reform bill currently before parliament if it passed. Under the rule, if the votes in favor of the leading alliance reach 42.5%, an additional 12.5% would be granted to achieve a 55% majority. In the case of a PD coalition with the centrist UDC party led by Pier Ferdinando Casini, the two together could surpass 40%, said the poll.