"The lowest-expenditure household group spends proportionally less than average on interest, alcoholic beverages, and purchase of new vehicles, and proportionally more than average on rent, household energy, telecommunication services, and property rates."
The new HLPIs also include mortgage interest, which is a significant part of many households' costs but is not in the CPI, largely because the CPI is used to define the Reserve Bank's inflation target and including interest rates would introduce an element of circularity.
So what do the data tell us?
For one thing, the cost of living has risen faster over the past eight years for superannuitants than for any of the other groups the statisticians consider.
The HLPIs paint a picture of widening inequality over the past eight years.
For them, it has risen 19 per cent since June 2008, compared with a 13 per cent rise for all households combined.
A key reason is that some 88 per cent of superannuitant households own their own homes (even if 12 per cent are still paying off the mortgage), so the big decline in interest rates since 2008 has not benefited this group much.
At the same time, superannuitants spend more on local body rates and insurance, both of which have risen faster than CPI inflation.
Beneficiary households have also experienced higher than average inflation: their HLPI has risen 16 per cent since June 2008. A key reason is that for a typical beneficiary household, rent accounts for nearly a third of spending, compared with 11 per cent for all households. Rent increases have outpaced the CPI over that period.
But a crucial difference between the superannuitant and beneficiary households is that New Zealand Superannuation is indexed to rises in the average wage rather than the CPI.
The measure of average weekly earnings used to adjust super has risen by 27 per cent since June 2008, implying a real rise in super of nearly 1 per cent a year after the 19 per cent rise in superannuitants' cost of living.
By contrast, the main welfare benefits are increased in line with the CPI, which has risen by 13.9 per cent during the period, when beneficiaries' cost of living has risen 16 per cent. In real terms, they have gone backwards.
We might note in passing that one of the possible measures the Treasury mentions from time to time, in the context of reining in the future cost of NZ Super, is to change the indexation from wage inflation to splitting the difference between wage inflation and CPI inflation. Had that rule been in place since mid-2008, the cumulative increase in the value of the pension would have been just 1.5 per cent in real terms, not 8 per cent.
Ranked by their spending, the cost of living increase for the poorest quintile was 18.2 per cent, or twice the 9.1 per cent rise for the highest-spending quintile.
The HLPIs paint a picture of widening inequality over the past eight years.
Whether households are ranked by income, or by expenditure, and divided into five equal groups or quintiles, the picture is the same: the cost of living has risen more for lower-income or lower-spending households than for higher-income or higher-spending ones.
So even if inequality in nominal disposable incomes has not increased much since the global financial crisis, it has widened in real terms over the same period.
Since mid-2000, the cost of living for the poorest quintile by income has risen 16.8 per cent, for the second lowest by 15.3 per cent, for the middle quintile by 11.4 per cent, for the second highest by 11 per cent and for the highest income quintile by 10 per cent.
Ranked by their spending, the cost of living increase for the poorest quintile was 18.2 per cent, or twice the 9.1 per cent rise for the highest-spending quintile. The latter group benefited from the big fall in mortgage interest rates: 83 per cent of them are homeowners.
Looking just at the latest year, to September 2016, the cost of living rose 0.6 per cent for the lowest-spending quintile, 0.3 per cent for the second lowest and 0.1 per cent for the middle quintile, while it fell 0.1 per cent for the second highest spending quintile and fell 0.3 per cent for the highest spending quintile.
There is, however, an element of that was then, this is now about this data.
In particular, the big downward trend in mortgage rates looks to be virtually, if not indeed entirely, over.
In June 2008 the weighted average mortgage interest rate was 8.8 per cent. By September this year it had fallen to just under 5 per cent.
The stock of mortgage debt has climbed in the interim. It is nearly half as large again as it was in mid-2008. Even so, the combined interest payable on that larger debt is around $2 billion a year less than it was eight years ago.
But the Reserve Bank's forward guidance in week's monetary policy statement indicates no intention of cutting the official cash rate any further. It also acknowledged a widening gap between the OCR and banks' funding costs.
