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Value of Building Work Put in Place: March 2013 quarter
Embargoed until 10:45am  –  05 June 2013
Data quality

Period-specific information
This section contains information about data that has changed since the previous release.

General information
This section contains information about data that does not change between releases.

Period-specific information

Sample errors

Estimates for the value of building work put in place are derived mainly from a sample survey and are therefore subject to sample errors.

 Sample errors for the March 2013 quarter
  Percentage of total value of work put in place
 Residential buildings 4.1
 Non-residential buildings 4.3
 All buildings 3.0

Sample errors quantify the variability that occurs by chance because a sample rather than an entire population is surveyed. The sample errors above indicate that there is a 95 percent probability that the true value of work put in place this quarter is the published estimate, within plus or minus the sample error.

Non-sample errors

These errors are variable across quarters and cannot be quantified. They can occur when data on building consent and survey forms is incomplete or incorrect or when it is incorrectly delivered, interpreted, or classified. Editing procedures aim to minimise their impact.

Non-response imputation

For building projects where no survey response is received, Statistics NZ imputes values for work put in place, based on responses for comparable projects.

 Non-response values imputed for the March 2013 quarter

Imputed value $(million)

Percentage of category value

Percentage of all buildings value

 Residential buildings 287 17.1  10.1
 Non-residential buildings 95   8.2  3.4
 All buildings 382 13.5 13.5

Low-value consents

These are residential building consents valued from $5,000 up to $45,000, and non-residential building consents valued from $5,000 up to $80,000. For these consents, it is assumed that:

  • the consent value represents the value of work put in place
  • consented work will be done during the month following issuing of the consent.

Low-value jobs are therefore valued directly from consents (after a one-month lag), rather than by postal survey. The following table shows the values included for the March 2013 quarter.

 Low-value consents included for the March 2013 quarter 
  Low-value consents $(million) Percentage of category value Percentage of all buildings value
 Residential buildings   55 3.3 1.9
 Non-residential buildings   44 3.8 1.6
 All buildings  100 3.5 3.5

General information

Data source

Values for building work put in place are obtained each quarter by a postal survey of builders or consent applicants. The survey is based on building consents data and is called the Quarterly Building Activity Survey (QBAS).

Survey design

Building consents are grouped each month into four value ranges for residential buildings, and four value ranges for non-residential buildings, as follows:

  • Highest-value range – for all residential or non-residential consents, builders or consent applicants are surveyed to obtain quarterly values for building work put in place.
  • Second- and third-value ranges – a sample of builders or consent applicants is surveyed and the quarterly values collected are rated up, to represent both surveyed and non-surveyed building work.
  • Lowest value range – the consent values are used to represent the quarterly value of building work put in place.

Surveyed building jobs that are not completed at the end of the quarter are surveyed again in following quarters until the work is finished.

The rating up of sampled values and calculation of sampling error are complex and depend on factors that differ for each value range and month of selection. For further information, contact info@stats.govt.nz or Statistical Methods, Statistics New Zealand, Private Bag 4741, Christchurch.  

Consistency with other periods

Year

Change in coverage

1989

From September 1989, building work is excluded if its consent value is below $5,000. This excluded work is estimated as being less than 1 percent of published values.
1993 From January 1993, the building consents system replaced the less extensive building permits system. This may have affected the consistency of the time series to some extent.
1996 From the September 1996 quarter, consent values for multi-purpose buildings are coded to one or more of the most appropriate building types. Multi-purpose buildings were previously added to miscellaneous buildings.

Interpreting the data

Constant price series (volumes)

Current values include both a quantity and price component, whereas constant price series (volumes) have had the effect of price changes removed. Removal of price change (deflation) leaves just the volume (or quantity) component, enabling comparisons across different time periods without the distortion caused by price inflation (or deflation).

Quarterly values for residential building work and non-residential building work are separately deflated by the residential buildings and non-residential buildings sub-indexes from the capital goods price index. The deflated quarterly values are expressed at a constant pricing level, using September 1999 quarter prices. Deflated values for all building activity are calculated as the sum of the deflated values for residential and non-residential building activity.

Price deflation is done before seasonal adjustment and estimation of trend values.

Seasonally adjusted series

Seasonal adjustment removes the estimated impact of regular seasonal events, such as summer holidays and pre-Christmas purchasing, from statistical series. This makes figures for adjacent periods more comparable.

The seasonally adjusted series are recalculated quarterly when each new quarter’s data becomes available. Figures are therefore subject to revision, with the largest changes normally occurring in the latest quarters.

The X-12-ARIMA seasonal adjustment program, developed at the U.S. Census Bureau, is used to produce the seasonally adjusted and trend estimates.

Seasonal adjustment in Statistics New Zealand has more information.

Trend series

Trend calculation removes the estimated impact of regular seasonal events and irregular short-term variation from statistical series. This reveals turning points and the underlying direction of movement over time.

The trend series are recalculated quarterly when each new quarter’s data becomes available. Figures are therefore subject to revision, with the largest changes normally occurring in the latest quarters. Revisions can be large if values are initially treated as outliers but are later found to be part of the underlying trend.

The X-12-ARIMA seasonal adjustment program is used to produce the seasonally adjusted and trend estimates. Irregular short-term variation is removed by smoothing the seasonally adjusted series using optimal weighted moving averages.

Comparison with building consent statistics

Building consent statistics provide an indication of upcoming building activity, but comparisons may be affected by variable timing and valuation differences, particularly following the Canterbury earthquakes.

More information

View more information about building work put in place   

Liability

While all care and diligence has been used in processing, analysing, and extracting data and information in this publication, Statistics NZ gives no warranty it is error-free and will not be liable for any loss or damage suffered by the use directly, or indirectly, of the information in this publication.

Timing

Our information releases are delivered electronically by third parties. Delivery may be delayed by circumstances outside our control. Statistics NZ does not accept responsibility for any such delay.

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