The bellwether seat of Eden-Monaro has been held by the ruling party for more than 40 years. Will it remain that way this time around?

One of the unique strengths of our model is that we can estimate the probability of a scenario like this from the electorate-level betting odds. You can’t do this with the betting odds for the overall election result. And doing it with national poll results involves a lot of poor assumptions about the size of swings.

We ran our model for both the maximum-covariance and independent cases and simulated lots of elections. We then looked at each election and counted up the number of times Eden-Monaro went with the party who formed government.

The electorate of Eden-Monaro. Source: Wikipedia

Converting these to probabilities, we got probabilities of 48% and 74% (for the independent model and maximum-covariance model, respectively) that Eden-Monaro will remain a bellwether seat at the 2013 election. In other words, if we assume no covariance, there is a 48% probability that Eden-Monaro will be won by the same party that wins the election. If we assume maximum-covariance, there is a 74% chance that Eden-Monaro will be won by the same party that wins the election.

What does this mean? Recall that the maximum-covariance and independent models are two extreme ends of a spectrum, so the true probability lies somewhere in between (although not necessarily right in the middle). So the true probability that Eden-Monaro keeps its bellwether streak going is somewhere between 48% and 74%, according to the betting markets. That means, at this stage, it’s more likely than not to stay a bellwether seat, but it’s very uncertain.

This is an interesting result since the betting odds in Eden-Monaro are currently favouring the Labor candidate Mike Kelly, despite the fact that overall the betting markets are pointing to a Labor defeat. If you made the mistake of treating probabilities inferred from betting odds as vote proportions, you would incorrectly conclude Eden-Monaro was on track to break its streak. Of course, we are still a long way from the election and things can change.

We’ll be looking at all kinds of other scenarios over the course of the campaign. Let us know if there’s one in particular you’d like us to look at.

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I would like to know how or whether me winning the seat would screw up your formulas for next time. It might happen!

Andrew Thaler, Independent EdenMonaro

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