An analysis of four major polls shows Labor is at its lowest two-party preferred rating since Kevin Rudd took the leadership
Kevin Rudd: Labor at new low. Photograph: ABC
An analysis of four major polls shows Labor is at its lowest two-party preferred rating since Kevin Rudd took the leadership on 26 June.
I’ve been pooling opinion poll results since 2000, using a reasonably simple statistical model to combine the Newspoll, Morgan, ReachTEL and Essential polls. Any one poll has only so much precision, so averaging the polls combines the information spread out through multiple, individual polls.
My model also corrects for inaccuracies specific to individual survey houses, exploiting the fact that the last federal election gives us a fixed reference point (the election result) against which to calibrate the model.
The model also exploits the fact that public opinion today looks a lot like public opinion yesterday. Even in an election campaign, voter sentiment changes reasonably smoothly. That is, my model averages over time and over survey houses, to produce a much more precise estimate than relying on any single poll.
I used the model to track the polls during the 2004 and 2007 Australian elections, and the Huffington Post used my model and analysis for poll averaging in the 2012 US presidential election campaign.
The four latest polls we have to feed to the model are as the follows:
Table: Guardian
Only the Morgan poll has Labor level level with the Coalition, and this is when preferences are allocated by respondents. If preferences are allocated as at the 2010 election (the industry default), then the Morgan estimate of Labor two-party preferred (TPP) falls to 49.5%.
The “poll of polls” based on this data puts Labor on 48.2% TPP, with a “margin of error” (a 95% credible interval) of +/- 1.4 percentage points.
Graph: Guardian
The probability that Labor’s current TPP support lies below its 2010 result (50.12%) is 99.6%.
This means we're seeing the lowest level of Labor TPP support since Rudd returned to the leadership. According to older figures from the same model, Labor’s post-Gillard TPP peak was 49.7% on 6 July.
I should caution against over-interpreting the precision that appears to accompany my model-based poll average. Modelling requires simplification and assumptions; I’ve detailed these methods in a longer piece that will accompany the poll of polls results elsewhere on the Guardian Australia site.
For now, we might argue about the exact level, but it is reasonably clear that Labor has “come off the boil”, as they are down by about 1.5 percentage points from the post-Gillard high recorded in the first two weeks after Rudd’s return.
48.2% TPP or thereabouts will see the Coalition win reasonably comfortably. Rudd and Labor have a month to try to move the TPP needle back closer to 50-50.
Table: Guardian
Technical details on the model will appear in a longer piece that will be accompany the poll of polls elsewhere on the Guardian Australia site. We’ll update this regularly as polls are released.
