More random reflections on the 2019 polls

Over the next few months, I will post some random reflections on the polls prior to the 2019 Election, and what went wrong. Today's post is a look at the two-party preferred (TPP) poll results over the past 12 months (well from 1 May 2018 to be precise). I am interested in the underlying patterns: both the periods of polling stability and when the polls changed.

With blue lines in the chart below, I have highlighted four periods when the polls look relatively stable. The first period is the last few months of the Turnbull premiership. The second period is Morrison's new premiership for the remainder of 2018. The third period is the first three months (and ten days in April) of 2019, prior to the election being called. The fourth and final period is from the dissolution of Parliament to the election. What intrigues me is the relative polling stability during each of these periods, and the marked jumps in voting intention (often over a couple of weeks) between these periods of stability.

To provide another perspective, I have plotted in red the calendar month polling averages. For the most part, these monthly averages stay close to the four period-averages I identified.

The only step change that I can clearly explain is the change from Turnbull to Morrison (immediately preceded by the Dutton challenge to Turnbull's leadership). This step change is emblematic of one of the famous aphorisms of Australian politics: disunity is death.

It is ironic to note that the highest monthly average for the year was 48.8 per cent in July 2018 under Turnbull. It is intriguing to wonder whether the polls were as out of whack in July 2018 as they were in May 2019 (when they collectively failed to foreshadow a Coalition TPP vote share at the 2019 election in excess of 51.5 per cent). Was Turnbull toppled for electability issues when he actually had 52 per cent of the TPP vote share?

The next step change that might be partially explainable is the last one: chronologically, it is associated with the April 2 Budget followed by the calling of the election on 11 April 2019. The Budget was a classic pre-election Budget (largess without nasties), and calling the election focuses the mind of the electorate on the outcome. However, I really do not find this explanation satisfying. Budgets are very technical documents, and people usually only understand the costs and benefits when they actually experience them. Nothing in the Budget was implemented prior to the election being called.

I am at a loss to explain the step change over the Christmas/New-Year period at the end of 2018 and the start of 2019. It was clearly a summer of increasing content with the government.

I am also intrigued by the question of whether the polls have been consistently wrong over this one-year period, or whether the polls have increasingly deviated from the population voting intention as they failed to fully comprehend Morrison's improved polling position over recent months.

Note: as usual I am relying on Wikipedia for the Australian opinion polling data.