Pollytrack, Week 25
Posted by Possum Comitatus on May 20, 2008
In an act of fortuitous timing coinciding with the first anniversary of this blog, Nielsen emerges from polling exile after their less than spiffy performance in their final poll estimate of the last election campaign.
Now having three pollsters to play with – Newspoll, Morgan Phone Poll (I chose to exclude Morgan face to face polls as they behave quite differently to the phone polls of the three pollsters) and now Nielsen, we can construct a rolling average of the three pollsters weighted by sample size to give us what should be the most accurate estimate of Australian federal voting intention.
The Pollytrack series is born.
The way it works is simple, each observation in the Pollytrack series will consist of the average of the most current polls from each of the three pollsters, weighted by sample size. So, for instance, as a new Newspoll gets released, it will replace the previous Newspoll in the three pollster weighted average.
The larger the sample size that a given poll has relative to the other polls that make up Pollytrack, the greater the influence that poll with have on the actual Pollytrack number.
So for the first Pollytrack observation, which is Week 25 of the governments’ term, the three polls are Morgan Phone with a sample size of 618, Newspoll with a sample size of 1141 and Nielsen with a sample size of 1400.
Crunching the numbers gives us a weighted average of primary votes being 46.5 to the ALP and 37.4 to the Coalition with a two party preferred weighted average of 57.2% to the ALP and 42.8% for the Coalition off a broad supersample of 3159.
At the end of each week, Pollytrack will be updated to accommodate whatever new polls get released. As time goes on, we’ll end up with a charted weekly series which I’ll stick up the top under a link called Pollytrack, as well as place the current Pollytrack estimate in the right sidebar at the top. That sidebar number should be updated on the day a new poll comes out (where possible), so if the situation arises where there are a few polls released during a given week, that number in the sidebar will change as each poll comes out. The number at the end of the week is the one we’ll use as our permanent Pollytrack value.
People have asked what the MoE on this thing is – that depends on the sample sizes of the three pollsters, but will nearly always be between about 1.6% and 2%.