Political pollster Galaxy says it will investigate why the son of a former Liberal MP was part of the audience at yesterday's Rooty Hill RSL Club forum.

Joel Scalzi, the son of former South Australian Liberal MP Joe Scalzi, was one of the undecided voters selected by the polling company to question Prime Minister Julia Gillard and Opposition Leader Tony Abbott in a town hall-style meeting.

He asked Mr Abbott what the Coalition could offer him as an unmarried voter with no children.

"All I've got is a big DVD collection," the 27-year-old said.