The Parliamentary Library released an interesting little bit of stuff the other day, Population change in Commonwealth electoral divisions, 2006 to 2007.

What makes this interesting is the way the data plays out with the data from the 2007 Election.

First up let’s do a chart (!!); we’ll plot the ALP TPP swing by electorate from the 2007 election against the growth in the size of the 65 year + age group in each electorate over the 2006/07 period. We’ll also run a LOESS regression through it to show how the regression line of best fit changes through the range of values of the ALP swing.

The patterns here are interesting – for seats that received a swing that was smaller in size than the average of 5.4% (which happened to be a majority of seats, as it was a chunk of seats with large swings that drove the average up), the percentage growth in the size of the 65 yr and older population in those seats was, on average close to the national average of the 65+ growth, which was 2.7%

However, in the seats where the swings to the ALP were greater than 5.4%, the percentage growth in the 65+ population increased above the national average as the ALP swing increased beyond its national average.

That black regression line tells the story – it tracks the national average in the growth of the 65+ age cohort until it hits the ALP swing average, than grows substantially as the ALP swing grows.

In those seats that had an above average swing, the growth in the population of the 65+ cohort over the 2006-2007 period either drove the big ALP swing directly, or correlated with something or some group of things that drove the big swings.

Keeping all that in your thought orbit, let’s now take a look at a different comparison of this same issue; whereas the above was comparing a flow (the change in the ALP TPP vote) to another flow (the change in the population 65 years and older), we’ll compare a stock (the actual ALP TPP vote) to another stock (the actual proportion of the population that is in the 65+ group) – and we’ll again do it by electorate.

There’s a moderate relationship here that we all know about – the larger the proportion of oldies in a seat, the higher the Coalition vote. We also know that this is a direct correlation from the polling we see; people over the age of 65 vote for the Coalition in greater proportions than any other age demographic.

But if we bring all this info together, it tells us that while the oldies still vote for the Coalition in large numbers, the geographic power of that demographic (or the spatial relationship between the 65+ demographic and Coalition vote, by electorate) broke down at the 2007 election. Not only did it break down, it in fact reversed itself to a degree.

It didn’t reverse itself enough to make up for the strength of the pre-existing 65+/Coalition vote relationship by electorate, but the flow (the change in the proportion of the 65+ population) reduced the Coalition benefit that is contained in the stock (the total proportion of the population over 65+). The Coalition lost substantial ground in this key piece of their demographic electoral geography.

Further food for thought is that the people that moved into the 65+ demographic aren’t even baby boomers – it will only continue to get worse for the Coalition.

If we further break down our comparison of flows vs flows (the change in the 65+ population vs. the change in the ALP TPP vote) into metro and non-metro seats, more interesting things emerge (and we’ll run a simple linear regression line through these)

The relationship in the metro seats between the growth in the 65+ age group and the size of the ALP swing is positive and highly statistically significant, but the same relationship in the non-metropolitan seats is statistically insignificant (as in, there is no relationship despite the slight angle on the regression line). This is important because it knocks out the “sea change” effect from our list of possible explanations. Most of the destruction of the Coalition superiority in the 65+ group is happening in the cities.

Next up – we’ll take a look at young families and the ALP vote to discover something quite astonishing (to me, anyway), and then bring these demographic discoveries together with some regression magic.

Continue to Part 2

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