Change to the method of calculating seasonally adjusted and trend series at September 1995 prices.
From the December 2006 quarter there will be a change to the methodology used to calculate the seasonally adjusted and trend series at September 1995 prices. This change is being made in accordance with Statistics New Zealand best practice.
Under the new methodology, the seasonal adjustment step will be performed after the figures have been deflated to create the constant price series. This will remove residual seasonality from the deflators. Previously, the current price series have been seasonally adjusted prior to the figures being deflated to create the constant price series.
The new methodology will be applied to all time periods since September 1995. The change in methodology will affect all series on tables 8 and 10 of the quarterly Retail Trade Survey releases, as well as the retail sales per head of population at September 1995 prices series on table 4. The new series will be given new series identifiers (see table below) to distinguish them from the old series.
The series on table 6 (Actual Retail Sales at September 1995 Prices) will not be affected by the new methodology. However, the series identifiers on this table will be changed to maintain consistency between the deflated series.
|
Old series identifier |
New series identifier |
Table 4
Summary by quarter |
S1S9D
S1SPPD |
S1S9K
S1SPPK |
Table 6
Actual retail sales at September 1995 prices |
S1A*D |
S1A*K
NB: the data in these series will be unchanged under the new methodology |
Table 8
Seasonally adjusted retail sales at September 1995 prices |
S1S*D |
S1S*K |
Table 10
Retail sales trend at September 1995 prices |
S1T*D |
S1T*K |
Where * represents a letter from A–X, or numbers 1 or 9.
The new series will replace the old series in the tables from the December 2006 quarter publication (15 February, 2007), and will be used for all analysis in the Hot Off The Press.
Tables containing the old series will be included in the December 2006 quarter Hot Off The Press and will be available on request until the September 2007 quarter.
Copies of both the old and new tables for the September 2006 quarter are attached as downloadable Excel spreadsheets for comparison purposes. These are accompanied by graphs indicating the differences between the old and new series for each retail industry.
For enquiries please contact:
Kate Jackett or Blair Cardno
Christchurch (03) 964 8700
Email: subannuals@stats.govt.nz