In every election, some votes cast are informal or invalid. The degree of informality is influenced by many factors. In Australia, these include compulsory voting, differences between the voting systems of the states and the Commonwealth, and sociological factors. A 2003 paper published by the AEC (Informal Vote Survey–House of Representatives 2001 Election) provided an extensive analysis of the causes of informal voting in Australia and reviewed the sociological factors that explain levels of informality.
This paper seeks to identify factors that influenced the increase in informal voting from the 2001 House of Representative elections to the 2004 elections (from 4.8% of votes cast to 5.18%). The paper examines the hypothesis that an increase in the number of candidates influenced the number of informal votes in 2004. The paper also looks at changes in the numbers and proportions of informal votes of different types from 2001 to 2004.