Monday, 31 July 2017

2016 Census Carwoola: Income in the Gazette area

My original aim for this post was to do a general post about what could loosely be termed indicators of affluence in the area.  However when I started to investigate the most obvious indicator of this - income - I found I had enough to say about that, without pushing the strength of the data beyond breaking point, to complete a post on its own so here we go.

Personal Income

The question on the form asks for people's income in ranges, defining the response categories in terms of weekly income and the annual equivalent.  That reflects the different ways people in different situations think about their income.  Personally, I always think of my income in terms of annual amounts (because that is how Commonwealth Public Service salaries were expressed and that is what ATO is interested in) so I will use those values in what follows.

I am unsure what happens now, but back in the day most of the ranges quoted on the form related to income levels of interest to people concerned with social welfare so tended to split up the lower levels.  Some other users were more interested in getting more detail on the big end of town to that they could identify just which postcodes were a good target for marketing the bigger BMWs and dodgy tax avoidance schemes but they were unlucky.  I'll return to this below when comparing 2011 and 2016.

In all of what follows I have expressed values as the % of cases in which an income was reported.  This excludes the categories "Not applicable" (mainly persons aged less than 15 years) and "Not stated".  The Not Stated rate is traditionally higher for this variable than many others but is very similar between the censuses for the Gazette area at 8.7% in 2011 and 9.1% in 2016.

The first chart shows the income profiles for the Gazette area and Australia for 2016.  My use of a trendline is simply to try to reduce the "noise" in the graph and reveal a general picture.
Clearly incomes in the Gazette area in 2016 are higher than for Australia in total.

Comparing 2011 and 2016 was made complicated by changes to the ranges appearing on the form between the 2 Censuses.  In some cases the change was simply a split of 1 class in 2011 into 2 classes for 2016 while for 1 case the boundary between 2 classes was changed and in another 2 classes in 2011 became 3 in 2016.  As clear as mud?  Perhaps a graphic will help!
So I plotted the profiles for 2011 and 2016 using the combined ranges.
 The shapes of the distributions are remarkably similar between the two years with a broad implication that incomes are higher in 2016 than in 2011.  Which fits with expectations.  Whether this is because of rises in remuneration rates for the same jobs or because residents have changed jobs to higher brackets is well beyond the scope of these data (let alone my ability to sort that out).

Within the Gazette area I examined the profiles by sex.
 I will simply note that I am surprised by the shape of the polynomial curve for females.  If readers can explain (or even hypothesise) what that means please put a comment on this post!

The other 'basic' demographic classification is age but trying to present profiles for 10 age classes and 15 income groups would be an incomprehensible  mess.  Rather, I decided to present information about the median income class for each 10 year age group.  That is, the income class where half people were in lower classes and half above it.  If anyone wants detail about that it can be provided but generally, "trust me I'm a statistician"!
This is essentially consistent with the chart above comparing overall profiles for income in the Gazette area and Australia.  Note that we have few residents aged 80+ and the Income Not stated  rate for that small group (27%) was much higher than for any other age class.

Household Income

As well as including data on the personal incomes reported on the forms the ABS adds up the incomes within a household (=dwelling) to give a household income.  There are a few nuances in this explained in the census dictionary but that is the principle.  Here is a chart showing the percentage of in scope dwellings according to income levels (I have plotted the upper bound of the income class for ease of presentation).
I have chosen line styles to emphasise the polynomials which cut out the "noise" in the series.  They are a pretty good fit to the underlying data as shown by the correlation coefficients.  My major takes from the chart are that:

  • the data points are clustered to the left of the chart, reflecting the user-interest in detail of the lower incomes; 
  • overall the shapes of the two series are similar, with a long 'tail' on the right of the chart; but
  • yet again the Gazette area has a higher proportion of people at higher income levels than Australia as a whole
Looking at the original data I am intrigued by the presence in both series of a marked peak for the income group $104k to $130k (plotted at $130k).  I can't at this stage work out, with certainty, why that is so but it is interesting that an annual income equal to twice Average Weekly Earnings for November 2016 is $120k right in the middle of that class.   I need to think about that a little more.


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