You know the author is actually involved with one of the "other" indices, don't you?
Yes, I agree with that.
Let's make the ABS system a bit more clear:
ABS guide for HPI
THen at the same link you have the reason of the metodology used and why (it make you wonder how APM and RP data can have accurate measure with different system...)The ABS commenced a review of the HPI in 2004. The objectives of the review were to:
! determine specific user requirements for a revamped HPI;
! identify possible data sources that were consistent and comprehensive;
! assess the costs and the strengths and weaknesses of these alternative data sources;
and
! develop a strategy to deliver an improved HPI.
Arising from the review, there were four important aspects of the data series identified as
needing to be changed or improved:
! the timeliness of the HPI release;
! the time at which prices are recorded – from settlement date to the date of
exchange of contracts;
! the effects of compositional changes – to be reduced by adopting a finer level of
stratification to take better account of compositional shifts: and
! the coverage of the index – to include ‘other dwellings’ (townhouses, units and
apartments), and dwellings covering the regions in each State outside the capital
cities.
Source: Australian Bureau of Statistics‘Constructing representative real estate price indices is challenging. Difficulties can arise
because real estate markets are heterogeneous, both within and across countries, and
illiquid. There may be no unambiguous market price. Moreover, such diversity and lack
of standardization results in the need to gather a wide range of data to compile indices
that are characteristic of the various market segments; this would contribute to high data
collection costs and may require greater technical sophistication. Representative real
estate prices in residential and commercial markets can be hard to measure accurately
given the small samples that are often available, as there may be disparate prices for
apparently similar properties and prices may be volatile.’
Although the IMF Guide does discuss a number of techniques, the material is not
comprehensive.
The central issue is how to utilise prices for an essentially heterogeneous set of dwellings
to construct measures of price change for homogeneous dwellings. There are three
general approaches that might be used to achieve this: hedonics, repeat sales and
stratification.
...
I hope this makes things a bit more clear (as usual you've got to go to the source to get the proper informations...)
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