Saturday, November 10, 2018

Updated poll aggregates

I have not done this for a while ... so here goes.

First the two-party preferred (TPP) aggregation. While there was substantial movement associated with the leadership change (late August), and some volatility thereafter during September, things have settled down to around or just below where they were for the Coalition at its worst under the former Prime Minister.

Note: for the TPP aggregation, all pollsters are included in the constraint of setting house effects such that they sum to zero.

A quick comparison with my house-effect adjusted moving average models (which don't have discontinuities built in).

Since upgrading to Stan 2.18, my former primary vote model stopped working. So I have simplified and refactored this model. As a result of the refactoring, the requirement that the four parties total to 100 per cent on every day is not longer enforced in the model. Notwithstanding this, the total is typically within in 0.2 percentage points of 100 per cent (a mean of 99.99 per cent and a standard deviation of  0.11 percentage points). 

I have also taken YouGov and Ipsos out of the sum-to-zero constraint for house effects (because they were producing primary vote estimates that differed substantially from other pollsters). As a consequence, these excluded pollsters only inform the shape of the aggregation. Their polls do not inform the vertical positioning of the aggregate on the charts.

Of note:
  • The leadership turmoil in late August and into September harmed the Coalition's primary vote, and other parties primary vote and helped the primary vote share for Labor and the Greens.
  • After the volatility of the leadership change, that is to say since the start of October, Labor's primary vote has strengthened; while the Coalition's primary vote has been stagnant. 

The medians from the above plots can be compared. The following plots have the medians adjusted so that they sum to 100 per cent exactly on each and every day.

And finally, a quick look at One Nation (which is included in "other" above). Note: I have excluded Ipsos from this analysis as its treatment of One Nation is inconsistent over time when compared with the other pollsters.

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