Background to the survey
The Wholesale Trade Survey (WTS) is designed to provide short-term economic indicators for the wholesale trade sector. In addition, the survey data is used to compile the wholesale trade sector component of quarterly national accounts.
The survey was last redesigned in the September 2002 quarter. For more detail about the redesign, refer to Wholesale Trade Survey – Redesign: September 2002, available on the Statistics New Zealand website. As a result of the redesign, a split between raw materials and finished goods stocks is now available. The analytical back series for each stock type has been calculated based on the ratio of raw materials to finished goods stocks collected in the September 2002 quarter.
The target population for this survey is all kind-of-activity units (KAUs) operating in New Zealand that are classified as Wholesale Trade (Australian and New Zealand Standard Industrial Classification Division F) on Statistics NZ's Business Frame.
The survey population is stratified according to:
- industries defined by the ANZSIC-based ANZIND classification at the inter-industry level
- size (in terms of the rolling mean employment number)
- turnover (annualised GST sales).
Each ANZIND inter-industry classification contains between two and four substrata. Because of the contribution large units make to the economic activity within each industry group, they are all included in the sample. A portion of the remaining medium to large units is also included in the sample. In addition, small to medium-sized businesses have their data modelled from administrative data (GST and EMS) sourced from Inland Revenue. All wholesaling KAUs belonging to a selected 'enterprise' are included.
About 1,300 units have been selected from the entire population for the postal sample, and the data for approximately 13,500 units is modelled from tax data
Sample maintenance is the process that maintains the sample over time, to reflect births, deaths and other structural changes identified on the Business Frame. The information for Business Frame changes can be from a variety of sources, including GST registrations and respondent contact.
New enterprises are identified when they register for GST. Once a quarter, the new enterprises are selected into the sample using the same criteria as for the original sample. These are referred to as births. When an enterprise ceases trading, its wholesaling KAUs are removed from the survey. These are referred to as deaths.
Enterprises can also enter or leave the survey sample if they are reclassifications from another industry to wholesaling. Reclassifications occur when an enterprise changes its main form of activity (eg from manufacturing to wholesale trade). These are usually identified in the Annual Frame Update Survey (AFUS) conducted in February each year.
The sample for the WTS is reselected each quarter to ensure that the sample reflects changes occurring in the wholesale trade population.
Errors in the survey are divided into two classes:
Non-sampling error includes errors arising from biases in the patterns of response and non-response, inaccuracies in reporting by respondents, and errors in the recording and coding of data. The size of these errors is difficult to quantify. Data is subject to revision if significant errors are detected in subsequent quarters.
Sampling error is a measure of the variability that occurs by chance because a sample, rather than an entire population, is surveyed.
An activity unit is included in an industry based on its predominant activity in terms of operating income.
The 16 industries are defined as follows:
|Unprocessed primary products
|Cereal grain wholesaling
|Farm produce and supplies wholesaling nec
|Petroleum product wholesaling
|Metal and mineral
|Metal and mineral wholesaling
|Building supplies wholesaling nec
|Farm, construction machinery, and professional business equipment
|Farm and construction machinery wholesaling
|Professional equipment wholesaling
|Business machine wholesaling nec
|Electrical and electronic equipment
|Electrical and electronic equipment wholesaling nec
|Machinery and equipment nec
|Machinery and equipment wholesaling nec
|Commercial vehicle wholesaling
|Motor vehicle new part dealing
|Motor vehicle dismantling and used part dealing
|Primary product food
|Poultry and smallgood wholesaling
|Dairy produce wholesaling
|Fruit and vegetable wholesaling
|Food and grocery products
|Confectionery and soft drink wholesaling
|Tobacco product wholesaling
|Grocery wholesaling nec
|Textile, clothing and footwear
|Textile product wholesaling
|Household appliance wholesaling
|Floor covering wholesaling
|Household good wholesaling nec
|Wholesale trade nec
|Photographic equipment wholesaling
|Jewellery and watch wholesaling
|Toy and sporting good wholesaling
|Books and paper product
|Book and magazine wholesaling
|Paper product wholesaling
|Pharmaceutical and toiletry
|Pharmaceutical and toiletry wholesaling
Australian and New Zealand Standard Industrial Classification system.
An ANZSIC-based classification used to group industries for publication.
A register of all economically significant businesses operating in New Zealand. The WTS population is drawn from the Business Frame.
A business entity operating in New Zealand either as a legally constituted body such as a company, partnership, trust, local or central government trading organisation, or as a self-employed individual.
Kind-of-activity unit (KAU)
A subdivision of an enterprise engaged in predominantly one activity and for which a single set of accounting records is available.
Rolling mean employment (RME)
RME is a 12-month moving average of the monthly employee count (EC) figure, which replaces the numbers of full-time and part-time employees.
Income from total sales. This includes:
- sales of processed goods
- sales of goods purchased for resale
- sales of services
- repair services
- processing fees
- management fees
- rental income
- leasing income
- patent fees.
Operating income excludes:
- interest/dividends received
- insurance claims
- government grants
- exchange rate gains
- extraordinary items
- gains on sales of fixed assets
- excise duties
- bad debts.
Closing stocks of raw materials for use in production, plus the closing stocks of finished goods, work in progress and trading stocks.
Seasonally adjusted series
The X-12-ARIMA package has been used to produce the seasonally adjusted estimates and trend estimates for sales in all subdivisions. 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 quarters more comparable.
All seasonally adjusted figures are subject to revision each quarter. This enables the seasonal component to be better estimated and removed from the series.
Restructuring within the dairy industry has affected the primary product food industry series in the September 2002 quarter. In order to maintain the long-term continuity of the seasonally adjusted and trend series for primary product food and total wholesaling, the actual series is adjusted prior to the seasonal adjustment program being run. This adjustment to the actual series removes the discontinuity in the series.
The X-12-ARIMA seasonal adjustment package is very robust. However, problems occur when there has been an abrupt change in the seasonal variation, as with other seasonal adjustment packages.
For any series, the survey estimates can be broken down into three components: trend, seasonal and irregular. While seasonally adjusted series have had the seasonal component removed, trend series have had both the seasonal and the irregular components removed. Trend estimates reveal the underlying direction of movement in a series, and are likely to indicate turning points more accurately than seasonally adjusted estimates.
The trend series are calculated using the X-12-ARIMA seasonal adjustment package. They are based on a five-term moving average of the seasonally adjusted series, with an adjustment for outlying values.
Trend estimates towards the end of the series incorporate new data as it becomes 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 quarter, but is found to be part of the underlying trend as further observations are added to the series. Typically, only the estimates for the most recent quarter will be subject to substantial revisions.
For more information, follow the link from the technical notes of this release on the Statistics New Zealand website.
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