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.

Saturday, June 27, 2015

A pox on both your houses

With yesterday's ReachTEL poll, we have recent attitudinal polling from the three houses that regularly do this kind of thing.

The pollsters agree: in the past month, the punters have marked down the performance of both leaders.

In a manner similar to the way in which we use a latent Dirichlet process to estimate the primary vote for each of the major parties, we can use a latent Dirichlet process to estimate the degree of happiness or unhappiness with the Prime Minister and the Leader of the Opposition.

If I could beg your indulgence with the traffic light metaphor for chart colours, the results follow:

And for the Leader of the Opposition ...


We can also plot the results for the Prime Minister (PM) and Opposition Leader (OL) side-by-side.

Tuesday, June 16, 2015

Updated aggregate

This week we have three new polls:

  • Ipsos has it at 47-53 in Labor's favour, a three point decline for the Coalition.
  • Morgan has it at 45.5 to 54.5 in Labor's favour, a two and a half point decline for the Coalition (based on preference flows at the last election).
  • Newspoll (the last in its current incarnation) has it at 49 to 51 in Labor's favour, a one point improvement for the Coalition.

Not surprisingly, with two polls making sizeable jumps in Labor's favour, we have seen the two-party preferred (TPP) poll aggregate collapse for the Coalition. 

What is a little harder to discern is whether this is just fortnight-to-fortnight noise, or something more significant. 

Net happiness with both the PM and Opposition Leader seems to be in decline.

Notwithstanding the latest Newspoll, Labor's primary vote appears to have stopped falling.

But the Coalition has fallen, and the Greens have increased significantly in the past couple of weeks. 

Sunday, June 14, 2015

The challenge of model specification

I have been playing with different models and I have reached a conundrum. My anchored primary vote model appears correct on paper, but yields a result inconsistent with other models. The anchored model seeks to locate the primary vote polls in terms of their performance at the last election. The unanchored model assumes that collectively the pollsters are unbiased (as a consequence, house effects sum to zero), and the average poll result is a good indicator of hidden voting intention.

The problem, in part, is the poor performance of the primary vote polls prior to the last election. The Greens vote was substantially down on what the immediate pre-election polls suggested. The Coalition and Other Party votes were substantially up.

Let's compare the primary vote charts for the election-anchored and sum-to-zero models. You will note that the anchored model has a wider credibility interval (and therefore offers less certainty around the median sample).

We can apply preference flows at the last election and the primary vote estimates from both models to estimate a Coalition two-party preferred result. Again we get different results.

Clearly, I have a bit more thinking to do on this.