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OTHER OUTPUTS AND DISSEMINATION
11.6 The number of transfers of established houses and attached dwellings provides an indication of the level of sales activity for each quarter.
11.7 From the March quarter 2015 publication, the ABS has used the CoreLogic RP Data residential property sales dataset, which includes real estate agents data to calculate the series from the March quarter 2014. There are differences in the numbers produced using the new data source compared to the previous data source (which contained VGs data only). Therefore, users should apply caution when comparing data prior to March quarter 2014 with data after March quarter 2014.
11.8 As the ABS receives more unit record residential property sales data, the median price of all established houses and attached dwellings transfers and the number of houses and attached dwellings transfers are revised as necessary. The usual practice is to update the most recent ten quarters of published figures.
Comparing Indexes to Total Value of dwelling outputs
11.9 Users should exercise caution in comparing price movements in the indexes and changes in the value of the dwelling stock and its components. The indexes are designed to measure the change in value of the stock of dwellings in the capital cities fixed at the last Census, whereas TVDS is designed to measure the current value of the dwelling stock in the States and Territories. As such, movements in the value of the dwelling stock are a result of changes in the price and quantity of dwellings. Movements in the indexes represents price change only.
Comparing Medians and Means
11.10 Users should exercise caution when comparing the unstratified median prices and the mean value of dwellings. The unstratified median price (for established houses and attached dwellings) of dwelling transfers over the reference period is the mid-point of all properties bought/sold in the period. In contrast, the mean value of residential dwellings, represent what the average dwelling value was in the reference period. Additionally, the mean values are calculated across the whole of state and for all dwelling types, whereas the medians are calculated for individual dwelling types and for the capital city and rest of state separately.
INTERPRETING INDEX NUMBERS
11.11 Movements in indexes from one period to any other period can be expressed either as changes in index points or as percentage changes. The following example illustrates the method of calculating index points changes and percentage changes between two periods:
June quarter 2015 index number = 154.0
less March quarter 2015 index number = 140.3
equals change in index points = 13.7
percentage change 13.7/140.3 x 100 = 9.8%
11.13 The percentage change between any two periods must be calculated, as in the example above, by direct reference to the index numbers for the two periods. Adding the individual quarterly percentage changes will not result in the correct measure of longer-term percentage change. In other words, the percentage change between, say, the June quarter one year and the June quarter of the following year will not necessarily equal the sum of the four quarterly percentage changes. The error becomes more noticeable the longer the period covered and the greater the rate of change in the index. This can readily be verified by starting with an index of 100 and increasing it by 10% (multiplying by 1.1) each period. After four periods, the index will equal 146.4 delivering a through-the-year percentage change of 46.4%, not the 40.0% obtained by adding the four quarterly changes of 10.0 per cent.
11.14 Residential Property Price indexes produced by the ABS are published with percentage changes calculated to illustrate two different kinds of movements in index numbers:
September quarter 2014 = 130.5
plus December quarter 2014 = 135.2
plus March quarter 2015 = 140.3
plus June quarter 2015 = 154.0
equals = 560.0
Financial year 2014-15 Index 560/4 = 140.0
11.16 The number of price observations available to compile the indexes each quarter depends on market activity. For the smaller capital cities (Hobart, Darwin and Canberra) there are occasions when strata have low numbers of price observations. Rather than suppress publication of the series they are included as the long term trends are considered reliable. Care should be exercised when analysing the indexes quarter-to-quarter movements of the smaller capital cities.
HISTORICAL SERIES AVAILABLE
11.17 As noted above, the HPI series compiled under the previous methodology (prior to the 2004 review) is published on the ABS website for users to access. This series commences in June quarter 1986 and concludes in June quarter 2005.
11.18 The ABS does not recommend linking the historical and the current series due to the different methodologies used.
11.19 The final decision for determining the appropriateness or otherwise of the residential property price indexes for any particular application lies with the end user. While the ABS can provide technical and statistical guidance, it does not provide advice on indexation practices, nor can it tell users which index would best suit any particular use. See Appendix 1, Use of Price Indexes in Contracts, for further information.
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