Estimate of New Dwelling Units: May 2000

Source of data

Data on building authorisations is obtained each month from all territorial authorities.

Dwelling units

Each dwelling unit in a housing project is separately counted.

Seasonally adjusted estimates

The X12-ARIMA package has been used to produce the seasonally adjusted and trend estimates in Table 1. Seasonal adjustment aims to eliminate the impact of regular seasonal events (such as annual cycles in agricultural production, winter or annual holidays) on time series. This makes the data for adjacent months more comparable. All seasonally adjusted figures are subject to revision each month.

From October 1998, X12-ARIMA has been used to produce the seasonally adjusted and trend estimates, rather than X11-ARIMA. X12-ARIMA is an updated version of X11-ARIMA, developed at the US Bureau of the Census. The methodology change has resulted in some additional revisions to previously released figures, due to the slightly different treatment of outliers in the newer package. The change has been implemented to ensure that the high quality of the seasonal adjustment process is maintained.

Trend estimates

For any series, the survey estimates can be broken down into three components; trend, seasonal and irregular. The trend series attempts to estimate the underlying behaviour of a series, and is likely to indicate turning points more accurately than the seasonally adjusted estimates. The trend series is produced by removing estimated regular seasonal effects in the data, and then smoothing this seasonally adjusted series to reduce the effects of short term variation.

The Dwelling Units trend series is calculated using the X12-ARIMA seasonal adjustment package. It is based on optimal weighted moving averages of the seasonally adjusted series with an adjustment for outlying values.

Trend estimates towards the end of the series incorporate new data as they become available and can therefore change as more observations are added to the series. Revisions can be particularly large if an observation is treated as an outlier in one period, but is found to be part of the underlying trend as further observations are added to the series. All trend estimates are subject to revision each month but normally only the last two or three estimates are likely to be substantially altered.

Release of final data

When the statistical information is fully processed in about four weeks, statistics on residential and non-residential buildings will be available including floor area, value, location of building and building type, eg farm building.

More information

For more information, follow the link from the Technical notes of this release on the Statistics New Zealand website.

Liability

Statistics New Zealand gives no warranty that the information or data supplied contains no errors. However, all care and diligence has been used in processing, analysing and extracting the information. Statistics New Zealand shall not be liable for any loss or damage suffered by the customer consequent upon the use directly, or indirectly, of the information supplied in this product.