6401.0 - Consumer Price Index, Australia, Sep 2012
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 24/10/2012
Page tools: Print All

APPENDIX 1 RE–REFERENCING THE CONSUMER PRICE INDEX

From the September quarter 2012, the ABS harmonised the index reference periods for the Consumer Price Index (CPI) series. These series are now presented on an index reference period of 2011-12 = 100.0.

The ABS has published conversion factors in 'Table 17 - CPI conversion factors, from index reference period 1989-90 to 2011-12' available as a data cube on the 'Downloads' tab of this product. This enables users to convert previously published time series to the new index reference period or to convert index numbers on the new index reference period to an old time series index reference period.

The following examples demonstrate the method used by the ABS to calculate the conversion factors to convert from the old (1989-90 = 100.0) to the new (2011-12 = 100.0) index reference period (and vice versa).

Converting a series to the current index reference period

The conversion of index numbers from an old index reference period to a new index reference period involves a rescaling of the index numbers. The conversion factors that should be applied to the index numbers are calculated by obtaining the ratio of the index numbers on the old index reference period (1989-90 = 100.0) to the new index reference period (2011-12 = 100.0). Index numbers for financial years are calculated as the simple (arithmetic) averages of the four quarterly index numbers for that financial year.

 All groups CPI, weighted average of eight capital cities, index numbers Index reference period Period 1989-90=100.0 (old) 2011-12=100.0 (new) 2010-11 March quarter 2011 176.7 98.3 June quarter 2011 178.3 99.2 2011-12 September 2011 179.4 99.8 December quarter 2011 179.4 99.8 March quarter 2012 179.5 99.9 June quarter 2012 180.4 100.4 Financial year 2011-12 (a)179.7 (b)100.0 (a) Index number for financial year 2011-12 (index reference period 1989-90 = 100.0) = (179.4 + 179.4 + 179.5 + 180.4)/4 = 179.7 (b) Index number for financial year 2011-12 (index reference period 2011-12 = 100.0) = (99.8 + 99.8 + 99.9 + 100.4)/4 = 100.0

A conversion factor is calculated as follows:

Rounded conversion factor = 100.0/179.7 = 0.5565

Index number for the June quarter 2012 (index reference period 1989-90 = 100.0) = 180.4

Index number for the June quarter 2012 (index reference period 2011-12 = 100.0) = 180.4 x 0.5565 = 100.4

The conversion factor may be used to convert any historical All Groups CPI, weighted average of eight capital cities index numbers to the new index reference period. Different conversion factors will be required for each index series.

Converting re-referenced series back to the previous index reference period

Similarly, to convert index numbers on the new index reference period back to the old index reference period will also require rescaling of index numbers. The conversion factors that should be applied are obtained by taking the inverse of the previously described conversion factor.

Using the example above, a conversion factor is calculated as follows:

Rounded conversion factor = 179.7/100.0 = 1.7970

Index number for the June quarter 2012 (index reference period 2011-12 = 100.0) = 100.4

Index number for the June quarter 2012 (index reference period 1989-90 = 100.0) = 100.4 x 1.7970 = 180.4

The conversion factor may be used to convert any historical All Groups CPI, weighted average of eight capital cities index number to the old index reference period. Once again, different conversion factors will be required for each index series.