Optional preferential voting seems to have reduced informality in Queensland and New South Wales. Informality rates have been very low since optional preferential voting was introduced in Queensland in 1992 (below 2.5%). New South Wales experienced high informality rates with changes to the formality rules in the early 1990s, but the last two elections have had informality rates of around 2.5%.
It should be noted that in states with optional preferential voting systems, a high number of voters go on to mark just a first preference on Federal House of Representatives ballots (44.57% of informal ballots in Queensland and 35.65% in NSW in 2004), rendering them informal. Partial preferential voting does not seem to have the same effect.
While South Australia has a full preferential system, incomplete preferences (usually '1 only') are completed with a voting ticket supplied by the candidate. In all State elections since its introduction in 1985, the rate of votes completed by voting ticket has been higher than the informality rate.
|Election||Total Votes||Informal||Ticket||Ticket and Informal||%Ticket||% Informal||% Ticket, Informal|
It seems that South Australia would have by far the highest informality rate in Australia (between 7 and 9%) if it did not have the voting ticket provisions in place. It is possible that first preference voting is high due to local knowledge about the ticket provision (despite the ban on promotion) or less focus on educating voters to number all the squares.
Changes to State electoral systems and formality rules have caused significant, and sometimes temporary, increases in informal voting. In the 1991 NSW election, informality reached a high of 9.3% after ticks and crosses were declared informal. The ACT experienced high informality in its first years of self-government, using the modified d'Hondt system, and again when it switched to the Hare-Clark system. WA's high informality in 1989 could have been due to changes to the Legislative Council voting system.