As mentioned in my previous post, New South Wales is the only Australian jurisdiction that uses optional rather than compulsory or full preferential voting for single member lower house elections. It is also the only state that data enters all lower house ballot papers and publishes the data for outside research.
Optional preferential voting (OPV) means that voters do not have to number a preference for every candidate on the ballot paper. A ballot paper requires only a first preference to be formal. All further preferences are optional.
If during the distribution of preferences, a ballot paper for distribution has no preference for a candidate remaining in the count, the the ballot paper is put aside as having “exhausted” its preferences. Exhausted ballot papers have no direct involvement in determining the winning candidate, but they have an indirect role in altering the winning post a candidate must pass to win. As explained below, OPV works in favour of leading candidates over trailing candidates.
This can be explained by comparing the maths of full versus optional preferential voting.
- Under full preferential voting, the winning candidate must achieve 50% of the formal vote after the distribution of preferences. The winning post of the votes needed to win is set at the start of the count and does not change.
- Under optional preferential voting, the winning candidate must receive a majority of the votes remaining in the count, that is the formal vote minus exhausted preferences. The winning post is lowered with each exhausted preference making it easier for the leading candidate to win by making it harder for the second placed candidate to catch and pass the leader.
The chart below shows the two-party preferred preference flows for minor parties and Independents at the 2019 NSW election.
I'll explain the political implications of the above graph inside the post. But if you want more detail of the preferences flows by electorate by candidate, or by party by electorate, you can find all the details in this pdf document I've prepared.
Read More »The Political Impact of Optional Preferential Voting – NSW 2019 Preference Flows