Tuesday, June 25, 2013

Technical adjustments

Up until February this year, Morgan provided three poll series: a regular (usually reported fortnightly) face to face series (which typically had a sizable pro-Labor bias when compared with other polls); a less-regular telephone poll series (which was more in line with other polls); and an infrequent SMS series. From March, Morgan replaced these various series with a single muli-mode poll, which has been comparable with other polling houses (but a touch over-dispersed for the sample size).

Of the three series, I had used two in my six-month, Bayesian aggregations: the phone series and the face to face series. With the effluxion of time, I dropped the Morgan phone poll some time ago. It is now time to drop the Morgan face to face poll from the aggregation.

To enable comparison, I will provide some side-by side charts of the current six-month aggregation with, and without the face to face poll. The first three charts include data from the five face to face polls in 2013.

The next three charts exclude the Morgan face to face polls.

Out of interest I looked at the aggregation with both the Morgan F2F and Essential series removed. I remain disturbed by the under-dispersion in the Essential poll series. I am also disturbed by the muted movement in the Essential series over time compared with the movement of other poll series. While it might be the case that Essential is right and the other polling houses over-state movements in public opinion; on the balance of probabilities, I suspect Essential is under-responsive.

At this stage, I will leave Essential in the aggregation. Given the polling, a displacement by 20 (or even 50) basis points is not that significant to the clarity of the overall result.

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