Sunday, September 1, 2013

Sunday update

Since the midweek update:

  • Today's Murdoch press has an undated Galaxy poll (with an unreported sample size) - 47-53 in the Coalition's favour - a percentage point movement to the Coalition
  • A ReachTEL poll with a status quo result - 47-53 in the Coalition's favour
  • The latest Morgan poll (with preferences allocated using 2010 preference flows) - 46-54 in the Coalition's point - a 1.5 percentage point move to the Coalition

Dropping all of this into our Bayesian model yields the following:

At this point in the blog, it is my normal practice to remind people that I anchor the above Bayesian aggregation with the assumption that the net bias across all of the polling houses sums to zero. You will need to come to your own view about where the actual level of collective systemic bias lies for all the pollsters. At the 2010 Election (with a different set of pollsters), the population voting intention was about one percentage point more in the Coalition's favour compared with the pollster average (see here). In light of the 2010 experience, it is arguably plausible to subtract (say) half a percentage point or more from the above aggregation to adjust for the collective systemic bias across all of the polling houses. [As an aside, you will note that Simon Jackman, who seeks to anchor his Bayesian models with respect to the outcome of past elections regularly produces an aggregated poll that tracks well below the vast majority of individual poll results].

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