Via Adam, Stubborn Mule has a further break down of the informal vote increase by state. It ranges from 0.95% in Western Australia to 2.42% in the ACT. The most populous states, NSW, Victoria and Queensland all registered around 2% or more increases. Stubborn Mule writes:

It is hard to escape the conclusion that the increase in informal votes reflects a protest vote arising from deep voter dissatisfaction with both major parties.

As Adam notes, there are a lot of parties in Australia. One of the things when faced with a ballot sheet is the number of parties and candidates that have to be ticked off and ranked as part of the preference system. So you become fully aware of the Greys, Greens, Guns, etc.

The US is not the same. It has a very strong duality, whether it is because the US allows for less strict party line voting - though that is changing at the national level with the Republicans - or because of some historical aspect to the American electoral system. Many towns and cities have made their elections non-political by banning the mention of political parties as a way around the duality. Between the advertising and the nature of the signs you can usually tell whether they are Republican, Democrat or Independent.

To the original issue; how do you explain the increase in informal voting this election which made up nearly 30% of the swing against the incumbents. There is plenty of party choice if you don't want to vote for the major parties and you can rank Labor and Liberal last if you want. Additionally there is choice within the Coalition too if you want to vote for a conservative viewpoint.

Is it disgust at the major parties, disgust with national politics, or disgust with Australian politics? The Australian political entity, which includes politicians and the media, probably need to be aware that breaking cultural norms like this, with increases in informal voting, often don't go back. Once the culture is broken (ie the experiment with picking kids up after school in Israel), it reaches a new equilibrium.

More Reading on Australian politics

• Australian Politics
• The fate of the Australian Democrats in the upcoming election
• State Level Innovation
• Double Dissolution Elections
• Malcolm Turnbull Retiring From Australian Politics
• Checks and Balances On Parliament Through A Separate Executive
• Andrew Bartlett on Privacy
• Rudd Out, Gillard In
• Making Sense Of The 2010 Australian National Election
• Informal Votes In the Swing Against Labor
• Informal Voting In The 2010 Australian National Election