Tuesday, June 30, 2015

Aggregated polling update

A few new polls to report:

  • ReachTEL moved a percentage point in the Coalition's direction between 13 May and 25 June to be 48 to 52 in Labor's favour
  • Morgan moved one and a half percentage points in the Coalition's direction in late June compared with early June, to be 47 to 53 in Labor's favour
  • Essential (which I don't feed into my aggregations) moved a percentage point in Labor's direction compared with the previous rolling weekly report to be 47 to 53 in Labor's favour

It would appear the Coalition's post February recovery has peaked and is now plateauing. 

If you take the unanchored TPP model  have been using for some time, we get an aggregated Coalition TPP estimate of 47.8 per cent.

But the usual caveat applies: I anchor the above 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.

If I anchor the TPP estimate to the previous election, and extend the period of analysis back a little to include polls immediately prior to the previous election, the result is a TPP estimate of 48.3 percent for the Coalition. Still not a winning position.

The problem with this approach is that the way in which pollsters calculate their TPP estimate has changed. Prior to the 2013 election, the TPP estimate from most polling houses was based on primary vote preference flows at the 2010 election. Since the 2013 election, their TPP estimate is based on primary vote preference flows at that election.

If I anchor the primary vote polling to the 2013 election and apply the preference flows at that election, I get a TPP estimate of 49.1 for the Coalition (from which a win is possible, but a long-shot). In part, this is because most pollsters were well off the money at the 2013 election with their primary vote estimates. All over-estimated the green vote and most under-estimated the Coalition vote. The late emergence of Palmer was a bit of a surprise to some. The problem with anchoring to a poor polling performance election is that it is likely that some (perhaps most) of the pollsters reviewed their practice and changed their approach following the 2013 poll.

The primary vote estimates from the anchored, latent Dirichlet process are as follows.

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