Graham,

Could the apparent aberration between the Newspoll result prediction and the Gippsland by-election result be related to voter turnout?

The Australian Electoral Commission's Virtual Tallyroom final results for the 28 June 2008 Gippsland by-election shows voter turnout as having been 89.68% of the 95,580 electors now enrolled. See: http://vtr.aec.gov.au/HouseDivisionFirstPrefsByVoteType-13813-213.htm

At the October 2007 Federal elections the voter turnout for Gippsland is shown as having been 95.67% of the 94,967 electors then enrolled. See: http://results.aec.gov.au/13745/Website/HouseDivisionFirstPrefsByVoteType-13745-213.htm

Could it have been that there was a particularly heavy concentration amongst those who failed to vote at the recent by-election, of an intention to otherwise support the government that actually was expressed in the form of votes for it at the 2007 Federal elections?

Note the six percentage points difference (a decline) in voter turnout between the Federal elections and the by-election. It would seem that if there was such a concentration of intention to support the government amongst those who failed to vote on 28 June 2008, the decline in turnout was sufficient to have accounted for the disparity between the Newspoll prediction and the official result.