Explainer: what are preference deals and how do they work

In the run up to the federal election, there is growing discussion of “preference deals” between political parties.

But what are preference deals and how do they work?

In Australian federal elections, voters fill in ordinal ballots for both the house and the senate. This means voters are required to number the candidates who appear on the ballot paper in order of their preference.

On House of Representatives ballots, voters must number every candidate on the ballot paper. Senate ballots meanwhile, afford voters the choice of numbering at least six party groups in above-the-line voting, or numbering at least 12 individual candidates below-the-line.