The informal vote
Posted by Possum Comitatus on January 24, 2008
Inspired by Mr Mumbles look into the nature and causes of informal voting at the last election (down at his January 15th entry), I thought we might break out the old stats box and have a little squiz ourselves.Peter got it dead right when he said:
“Broadly, three things are likely to lead to, or are associated with, informal voting: optional preferential voting at the state level; high numbers of people from non English speaking backgrounds; and lots of candidates.”
For this, what we’ll do is regress the informal vote as a percentage of votes cast in each electorate against:
- The proportion of persons in the electorate who speak English not well or not at all as measured by the last census. We’ll call this variable NES.
- The number of candidates that stood in each electorate, we’ll call this variable, surprisingly, CANDIDATES.
- A dummy variable that has the value 1 for those States that have optional preferential voting at the State level, and a value of zero for those States that don’t. Qld and NSW have optional preferential, and SA has a strange ticket voting system that mimics the effects that OPV has in NSW and Qld on the informal vote (I tested it independently) – so we’ll classify SA as an OPV State as well. We’ll call this variable STATEOPV.
So running the regression on all 150 electorates we get:
The “C” is a constant that needs to be added into the equation (the value of which is calculated by the regression software mathematically) which tells us what the level of the informal vote would be should the other three variables equal zero. In this particular case, having zero candidates sounds a bit silly, but it’s a necessary procedure that gives us a statistical baseline to work from and only sometimes can the value of the Constant be taken and used literally. This is not one of those times.
So what this equation result tells us is that for every 1% increase in the proportion of people in the electorate that speak English not well or not at all, the informal vote goes up on average by 0.3%.
For every additional candidate on the ballot paper, the informal vote goes up by 0.2% and States with optional preferential voting at the State level experience, on average, an additional 1% increase in their informal vote compared to those states without OPV.
All these results are highly statistically significant, and collectively explain about 56% of the variation in the informal vote – which for cross sectional data like this is a pretty high level of real world explanatory power.
The NES variable is by far the most important, explaining about 34% of the variation of informal voting just by itself. If we run a scatter plot of the informal vote vs NES by electorate, we get:
To the naked eye that looks pretty linear, in that as NES increases, the informal vote proportionally increases – but for those of you that have stared at enough scatter plots, you might notice that there is actually a fair degree of non-linearity involved in the relationship.
As the proportion of people who speak English poorly or not at all in the electorate increases, there is a slightly disproportional increase in the informal vote.
After testing, if we use just NES as a variable against informal, NES explains about 34% of the variation in informal voting, but if we use the square of NES, that explanatory power jumps to 41%.
This seems to suggest that when an electorate contains a large community or communities of people with an NES background, rather than just clumps of people with NES background, informal voting really starts to jump. This is probably a good argument for the AEC to pester the new government for some extra money – electoral education programs in local community foreign language newspapers and media looks to be a good place to start if we want to lower the level of informal voting.
Similarly, after further testing, the number of candidates standing in an electorate doesn’t enjoy a linear relationship with the informal vote level either, it behaves similar to NES in that there is a disproportional increase in the informal vote with the more candidates you get standing in an electorate, although the statistical relationship is ever so slightly different in its shape.
So accounting for these slight non-linearities, our new equation becomes:
Which has increased the explanatory power up to over 60% simply by accounting for the disproportional effect that increasing numbers of candidates and increasing levels of NES have on the informal vote level.
Next post: some more on this informal vote, how decreasing the informal vote level would win the ALP more seats and where (so expect to see the AEC receive some new education program funding) and some funny relationships between party votes.
After some handy advice from Antony over SA state voting behaviour and a few other things, the above needs a bit of an adjustment. We’ll drop the CANDIDATES variable and simply use CANDIDATES^2 in isolation, as well as remove South Australia as a state that has an OPV effect polluting the informal vote in Federal elections in SA. There still seems to be something going on with the way the informal vote behaves as a function of the number of candidates – hopefully we can ferret out the causes of that underlying behaviour over the next few weeks. So the new working equation becomes: