This election will see a record number of candidates on the ballot paper for the House of Representatives, with 1203 candidates running, up from the previous record of 1188 in 2013.

In this post I’m analysing the relationship between the size of the ballot paper and the informal rate, in anticipation of voters having more difficulty filling out a formal ballot in 2022. Informal rates do become worse when voters are presented with more candidates, but that’s not the whole story.

Under the compulsory preferential voting (CPV) system used for the federal lower house, voters are required to fill out preferences for all candidates.

In practice this means you need to fill out consecutive numbers with no duplicates or missed numbers for every candidate (although you can skip the last candidate).

CPV, combined with compulsory voting, tends to produce a much higher informal rate than in other countries where casting a ballot is voluntary and easier.

The Australian Electoral Commission (AEC) used to publish reports after each election where they would survey informal ballots to categorise them based on why the vote was informal: was it blank, were the numbers incomplete, or were the numbers non-sequential. The last such report was published after the 2016 election.

Approximately half of the informal votes appear to be deliberate informal votes, including blank ballots and “scribbles, slogans and other protest vote marks”. Most of the rest appear to be accidental votes: incomplete numbering, non-sequential numbering or ticks and crosses. Most of these votes would be considered formal under the optional preferential voting (OPV) system used for New South Wales state elections.

The task of casting a formal vote gets steadily more difficult as the number of candidates increase, since you need to number more boxes without making a mistake. This is the theory underpinning my analysis: more candidates makes the task of voting more difficult, and thus results in more informal votes. Let’s find out if that’s true.

To start with, this first chart gives a sense of the number of candidates running in each contest over the last three decades.

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You can see how many more electorates there are with double-digit nominations in 2022. 28 seats have 10+ candidates, compared to 6 in 2019, 26 in 2013, and just three in 2010.

So if higher candidate numbers increase the informal rate, that has implications for the informal rate at this year's election.

Next up, I've grabbed the number of candidates in each contest at the last four federal elections, and plotted that against the informal rate in each of those contests.

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There's a clear trend of informal rates being higher with more candidates, but there are exceptions. The trend is most obvious at the lower end. While there are cases of informal rates around 2% where the number of candidates is 6 or less, you don't see those when there are ten or eleven candidates.

I've highlighted contests in New South Wales, and the stand out really clearly. While there are some high informal rates in contests with low candidate numbers, they are almost exclusively in New South Wales. Of 37 contests with an informal rate over 9%, 35 were in New South Wales.

I thought I'd simplify things here by just looking at the *average* informal rate for each state depending on the number of candidates running. There wasn't enough contests in the smaller jurisdictions, so the chart just features the four most populous states. I also limited the range of candidate numbers to exclude the rare 12-candidate contests and beyond.

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The average informal rate in Victoria, Queensland and Western Australia steadily increases with more candidates, levelling out around 6-7% once you get to ten candidates.

That is not the case in New South Wales, where the trend line is pretty much flat. Contests with 5-7 candidates had similar rates of informality to those with ten candidates.

So at this point I return to the AEC's 2016 informal rate survey, which has quite a lot of detail about different types of informal voting.

The electorates with the highest informal rates, which are mostly in the suburbs of Sydney, tend to have higher proportions of informal votes that are assumed to be unintentional, compared to informal voting nationwide. These seats don't have particularly large numbers of candidates: Werriwa had just four candidates, yet ranked in the top ten, while five others had five or six candidates.

It appears that there are other factors going on in these Sydney seats. They have optional preferential voting at a state level, which can lead to confusion. They are also seats with a great deal of cultural diversity. Some voters may not understand English. Other voters may be perfectly capable of understanding English but just don't understand Australia's complex voting system. The 2016 report found a strong relationship between the ABS Index of Relative Socio-Economic Advantage and Disadvantage (SEIFA IRSED) and the informal rate amongst Sydney electorates.

So candidate numbers is not the only factor in the informal rate, but it appears to be a major factor outside of New South Wales.

So how are things looking in 2022?

We know that candidate numbers have hit a record high, with voters in 28 seats having to choose between ten or more candidates. This next chart shows the average number of candidates per seat for each state or territory at the last five elections.

The average number of candidates in New South Wales is one of the lowest in the country, even with Queensland and the Northern Territory on about 7.5 candidates per electorate. The ACT is lower, with just six candidates per seat.

South Australia and Tasmania have jumped from ranking quite low in recent elections to having well over 8 candidates per seat in 2022. Victoria had the most candidates per seat at the previous record level in 2013 (9.3 candidates per seat) and now have just 8.4. Western Australia took the lead in 2019, and has maintained its lead, with 9.4 candidates per seat this year.

This is possibly the worst outcome for the informal rate - the increase in candidate numbers is concentrated in states where it is a bigger factor in the informal rate, while in New South Wales the informal rate doesn't need increased candidate numbers to be relatively high.