Many of the patterns of informal voting at the 2010 House of Representatives elections were similar to those observed at previous elections. For example, informality rates were highest for voters in New South Wales, with the 10 divisions recording the highest informality rates all located in Sydney.
The largest single category of informal ballots in 2010 was those with incomplete numbering (number '1' only and other incomplete numbering). However, for the first time the proportion of blank ballots was higher than the proportion of number '1' only ballots. Together, blank and incomplete ballots comprised more than half of all informal ballots at the 2010 House of Representatives election.
While the informality rate for blank ballots doubled between the 2007 and 2010 elections, levels of assumed unintentional informal voting (ballots with incomplete numbering, non-sequential numbering, ticks and crosses and those where the voter has been identified) continue to be higher than levels of assumed intentional informal voting (all other informal ballots).
There are many factors that could influence a voter to intentionally or unintentionally cast an informal vote and it is not possible, in many cases, to accurately quantify or even separately identify the impact these factors might have. Of those factors identified as significant influences on informal voting at previous House of Representatives elections, English language proficiency and the number of candidates appear to be the strongest predictors of informality rates or changes in informality rates in 2010. Analysis relating to differences between state and territory electoral systems and the federal system provided mixed results, suggesting that other factors were more significant influences on informality in 2010.