Tuesday, July 21, 2015

Aggregated poll update

There were two published polls since the last aggregation:

  • Today's Australian has the second new Newspoll at 47-53 in Labor's favour. This is a one point move in Labor's direction over the previous fortnight.
  • Last week's Morgan poll at 49-51 in Labor's favour. This was a 2.5 points move in the Coalition's direction over the previous fortnight.

In the following aggregations, because Morgan exhibits a higher variance than its reported sample sizes would suggest, I have arbitrarily down-weighted the sample size in the aggregation to 1000 respondents.

The unanchored aggregation is 47.7 points in Labor's favour. In trajectory terms: the government recovered ground quickly after its late-January/early-February troubles, and enjoyed a rare small post-Budget bump in May. Since then things have not changed much in terms of its share of the two-party preferred voting share. If an election were held now, the government would lose.

At this point, it is customary to remind my readers the unanchored model assumes that collectively the polling houses are unbiased (as a consequence, their collective house effects sum to zero), and the average poll result is a good indicator of the population voting intention. In practice, this is an oversimplification.

You will note that the error bars are much wider at the end of this fortnight's chart (above). The model has not yet got enough data from the new Newspoll (Npoll2) to locate its systemic house effect. Until we have a good number of new Newspoll results, the new Newspoll will be less influential in locating the aggregated poll result. We can see the wide range of house effects being applied to the new Newspoll in the next chart (below).

Looking at the primary votes, we see some unusual results. Compared with recent trends, the latest Newspoll was kind to Labor and unkind to the Greens. The rise of the Green vote over recent months appears to have come to an end.

Note: in all of the primary vote aggregations, I model the data on a week to week basis, rather than a day-to-day basis as I do with the two-party preferred vote shares. I plot the aggregation for the first day of the modeled week. As a result, there are data points after what looks like the end of the aggregation plot. Be assured, these data points were included in the analysis.

Finally, let's look at the aggregated attitudinal polling where, in spite of today's headlines, not much has changed. Please note, this is also modeled on a week-to-week basis.

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