6461.0 - Australian Consumer Price Index: Concepts, Sources and Methods, 2005  
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Contents >> 8. Collection Methodology


8.1 This Chapter describes the collection methodology used in the Australian CPI, with general collection issues discussed initially, followed by more detailed explanations of collection methods and procedures related specifically to each of the 11 CPI groups.


8.2 To achieve the Australian CPI conceptual objective of measuring pure price changes over time, regular monitoring of the prices of goods and services acquired by the CPI population group will obviously be necessary. However, it is not possible in practice to price every single type or variety of good and service purchased by the CPI population group at each collection cycle. The ABS overcomes this practical problem by using purposive sampling procedures, where representative sets of goods and services are selected for regular pricing. Similarly, it is not practicable to observe the prices of the selected goods and services in all retail outlets selling these items to the CPI population group. Again, the ABS uses purposive sampling to select a representative sample of outlets at which to price the selected items in each collection cycle.


8.3 The goods and services included in the CPI pricing samples are selected carefully to represent the range of types, varieties, etc. of goods and services bought by the CPI population group. Selection is made only after obtaining detailed information about the buying habits of the CPI population group, such as which varieties and brands of products are the largest selling types or which packaging sizes are most commonly used. This process involves extensive consultations with retailers, manufacturers, importers, government authorities, professional and trade associations and so on. In selecting the items to be priced, the following factors are taken into consideration:

  • The relative importance of the expenditure class in relation to the total CPI; in general, the more important the expenditure class, the larger the number of items priced.
  • The degree of homogeneity in the range of goods or services covered by the expenditure class; the more homogeneous the range, the fewer the number of price indicators required.
  • The extent to which the various products covered by an expenditure class are subject to different influences and cost pressures, likely to result in disparate movements in prices.
  • The likelihood of the particular type of good or service continuing to be available on the market for a reasonable period of time; in general, it is preferable to price the same specific items for a reasonable length of time rather than having to change price indicators regularly when particular goods or services appear and then disappear after only a short time in the market.
  • The extent to which the item can be defined and described clearly and unambiguously, to ensure that the selected goods or services can be priced to constant quality over time; for example, in pricing confectionery, it is likely that packaged, brand-name chocolates would be easier to price to constant quality over time than loose chocolates with no identifying brand name.

8.4 After the items to be priced have been selected, detailed specifications are prepared to ensure that all staff involved in price collection and compiling the CPI have exactly the same understanding of which particular items are to be priced. In most cases for goods, it is a relatively straightforward matter of specifying the characteristics involved in describing the items. The characteristics may include brand name, material of composition, model number, style, size, colour and type of packaging.

8.5 As discussed in Chapter 7, it is generally more difficult to specify service items adequately because both quantity and quality are less readily describable for these items. In addition, more detailed descriptions are usually required in the specifications for services in comparison to those for goods. For example, the specification for a can of tomato soup would consist of only two characteristics: the brand name and the weight of the can. However, the specification for a travel service like a bus fare will have to include three characteristics: the age of the purchaser (as both adult and child fares will be required), the specific route priced and the time of the journey (peak or off-peak fare).

8.6 The preferred practice in pricing goods for the CPI is to price identical specifications (i.e. the same brand name, size or model of product) at all outlets in all cities. The nature of many goods and services, however, makes this impossible for a large number of cases. In practice, products are categorised into one of three categories:

i. National standards. These products are available in all cities and at the vast majority of respondent outlets. They can be readily and clearly defined by characteristics such as make, model and size, as a specification for use nation-wide. Field officers have no latitude in choosing the product for pricing. Examples include motor vehicles and major brand breakfast cereals

ii. Respondent standards. In these cases, the product can be readily defined with regard to form and function but a multitude of brands and models may exist making it virtually impossible to guarantee that any one example of the product will be available Australia-wide. A generic description is provided in sufficient detail to ensure that the field officers will be able to locate an example of the product, consistent with the quality of those chosen in other outlets within the one city and broadly consistent with those in other cities. An example of the required type of product is chosen at each respondent outlet and its defining characteristics are added to the generic description for future use at the particular respondent. Examples of such products are beer, daily newspapers and furniture

iii. Volume sellers. For some products, there are a very large number of brands or varieties available and these are fairly readily substitutable for one another. In general, consumers show no, or minimal, brand loyalty or preference and base their choice purely on price. In these cases, brand is not considered a vital characteristic and the field officers collect the price of the best selling brand available from each respondent. Examples of these products include butter, frozen chickens and inexpensive varieties of spirits.

8.7 From time to time, major changes in existing products and services take place or new products and services become available on the retail market and begin to account for a significant share of household expenditure. Some examples in recent years are DVDs and electronic games. In such cases, careful consideration is given to whether these new goods or services should be priced for the CPI.

8.8 If a new product or service is deemed to be a completely different category of product (i.e. a new expenditure class) from any of the goods and services already included in the CPI, its inclusion would be considered only during one of the periodic review and re-weighting exercises. The inclusion of television sets in the 1960s is a good example of such an occurrence. However, where a new product or service falls within the definition of an existing expenditure class (e.g. the introduction of colour television sets or mobile telephones), the issue is when and how to introduce the product into the process of regular measurement of price movements for the CPI. Normally, the decision is made after consideration has been given to the following factors:
  • The product's share of the market: this has to be substantial before there is any point in introducing a new item.
  • Whether the product is firmly established and expected to become a permanently significant item of expenditure, rather than merely enjoying high sales temporarily because of novelty value.
  • Whether a normal price structure has been established, i.e. a price structure that is not unduly influenced by factors such as prestige, novelty value or relative scarcity of the product.

8.9 In general, a conservative approach is applied when dealing with the introduction of new products or services into the CPI. They are introduced into existing expenditure classes only after it is deemed that they have become widely available to the buying public, have become a permanent feature of household expenditure and that the price structures of these items are free from high premiums due to novelty value or scarcity of the item. All introductions of new items are handled by splicing the new item into the index so that its introduction does not, of itself, affect the level of the index.


8.10 Consumers purchase the goods and services priced in the CPI from a wide variety of retail outlets. Examples of these outlets include department stores, hotels, motor vehicle dealerships, doctors’ surgeries, electricity and gas shopfronts, travel agencies, schools and child care centres. For every item selected for pricing, the main types of outlets from which the CPI population group buys the items need to be identified so that the ABS can select representative samples of these outlets.

8.11 In selecting outlets for inclusion in samples for the CPI, the following factors are taken into account:
  • The relative importance of the expenditure class in the CPI. In general, the more important the item is (i.e. the larger the expenditure weight), the larger the sample.
  • The number of suppliers of the good or service in the city concerned. Generally, the larger the number of suppliers, the larger the sample. In some cases, however, there may be only one supplier, such as a city council or transport authority.
  • The degree of dispersion in prices among outlets. Where the expected dispersion of prices is large, the sample will need to be large. For example, a large sample of petrol retail outlets is usually needed because of wide variations in prices as a result of discounting practices. In the case of newspapers, a small sample is sufficient because standard prices are generally adhered to.
  • The geographical spread of outlets. As far as possible, the samples are selected to cover the main areas in which households from the CPI population are known to make their purchases.
  • The ownership of chains of outlets. Large retail chains frequently have a common Australia-wide or state-wide pricing policy. In these cases, pricing one outlet in the chain would be considered sufficient to obtain a representative estimate of price movement for that chain but the usual procedure is to have a number of observations in the samples commensurate with their overall market shares.


8.12 The samples of respondents are reviewed regularly to ensure that they remain representative of the CPI population group's sources for purchases. Events such as company takeovers, new retailers entering the market, existing chain organisations opening new outlets or new shopping complexes opening up can all lead to the need to change the samples of respondents so that they continue to be representative of the CPI population group's overall purchases. Changes to the sample of respondents or specifications are carried out using a splicing process. A worked example of this process is presented in Chapter 3.


8.13 A range of different methods is used to obtain price information; each method is designed to ensure the accuracy of prices used in the CPI. The majority of price information is collected via personal visits to the selected respondents. These personal visit collections are made by trained and experienced ABS field staff, who observe actual marked prices as well as discuss matters such as discounts, special offers, and volume selling items on the day, and record this information in handheld computers. The regular personal visits by field staff to the retail outlets also enable the field officers to continuously monitor activity in the market (such as market shares or possible quality changes). This information is used in maintaining sample representativeness, making quality change assessments and so on.

8.14 Once items have been selected they are organised into groups (called collections). Each collection contains products that are generally sold by all potential respondents and are also usually located together within any one store. An example of a collection would be a 'white goods' collection. This would contain refrigerators, washing machines, dishwashers and clothes dryers. Most respondents that sell any of these products will sell all of the products. These products are also usually located in the same area of any store.

8.15 The main benefits gained from grouping items within these collections are:
  • maintenance of representative samples is easier, as generally all potential respondents are able to supply all prices
  • the effort required by field officers to maintain collection itineraries is minimised.

8.16 The grouping of items into various collections is based on the situation faced by consumers in the market place, not by any ordering required for index estimation. The collection and use of alcohol prices provides a good example of this. Alcoholic beverages of all types are sold in two ways:
  • as individual drinks for consumption on the premises
  • in containers for consumption off the premises of the vendor.

8.17 Once collected the prices are re-sorted into the CPI compiler’s perspective i.e. categorised by alcohol type (beer, wine and spirits) for use in index estimation.

8.18 The ABS does not use list prices or recommended retail prices without checking that these are, in fact, the prices charged to customers by the respondent concerned. Special prices and discount prices are taken into consideration when these are generally available to the buying public. The basic test of whether such prices can validly be used in compiling the CPI is whether the goods are of a quality identical to that in the item specifications (e.g. the goods are not damaged or superseded stock) and are available in quantities sufficient for shoppers generally to buy them on the pricing date (i.e. there are not merely a limited number available to early birdshoppers or purchases are not subject to some other restriction).

8.19 While special and discounted retail prices are readily observable for the majority of goods, it is not necessarily the case for large and expensive durables, in particular motor cars, as prices sometimes may not be advertised widely and may be disguised in the form of bonuses (so-called trade-ins, extra features, etc.). In such cases, substantial effort (including interviews with senior sales staff) is made to ensure that full particulars of the actual transaction prices are obtained.

8.20 In cases where prices are set centrally and do not vary by location, the prices are collected from the supplier's head office. Postage charges are a good example of this situation.


8.21 In some cases, it is not possible to collect the price of a certain item in a particular period. This can be due to various circumstances, with a common one being the item was out of stock in the outlet sampled. The section on temporarily missing price observations in Chapter 3 describes several ways of dealing with this situation. The procedure most commonly used in the Australian CPI is to impute a movement for the missing item based on the price movements of the other items in the sample. The implicit assumption behind this procedure is that if it had been possible to collect the price of this item, its price would have changed in line with similar items. In most cases, this is a reasonable assumption and will provide an acceptable outcome for the index.

8.22 This method would be inappropriate when a product has no close substitutes or if its price is reviewed (and collected) annually. In these cases, a more appropriate method of imputation is to repeat the previous price.


8.23 Price editing commences during the actual collection process. The handheld computer used to collect the prices has a number of facilities designed to help the field officers edit the data as it is being collected. Examples of these edit checks include:
  • immediate calculation of the percentage change in price for the item
  • a facility for storing annotations about the price, such as notes from a discussion that they may have had with store staff about a change in the price
  • a facility for entering an edit symbol that describes the change in price; the edit symbol descriptor must be consistent with the price movement (for example, if a price fall for an item occurs because it is on special, the edit symbol accompanying the recording of the price will identify that this is the reason for the price fall).

8.24 Further editing checks, mainly to do with overall consistency, are performed back in the office.


8.25 Field officers are able to enter all the information necessary for quality adjustment to prices into the handheld computers.

8.26 If the field officers find themselves in a situation where they do not have all the information necessary for a successful quality adjustment calculation, then the record is flagged as such and dealt with by the index compilers.


8.27 The collected prices undergo further checking by the staff responsible for compiling the index. Where prices are found to be unusual (for instance, when movements are not considered representative) or not within expectations (i.e. inconsistent with knowledge gained from other sources), they are generally referred back to the field officer for verification.

8.28 Investigations are conducted to enable quality adjustments to be performed on records flagged by field officers as having quality changes which were not readily quantifiable.


8.29 The weighting pattern for the Australian CPI is based on the acquisitions concept and so the pricing of goods and services is also based on this conceptual approach for consistency (refer to Chapter 4 for an explanation of the different conceptual bases). In most cases, the acquisition of the good or service occurs at the same time as the payment and so any price movements are recorded then. There are some goods and services where payment for, and acquisition of, the good or service do not coincide. In these cases, prices are recorded at the time the good or service is acquired and not when the payment is made. Examples where this can happen include:
  • Goods and services invoiced periodically after consumption (such as electricity and telecommunications, and home delivered newspapers). Price movements are introduced into the index calculation from the date at which the price change is effective. Providers are therefore approached for price information regularly to obtain current charges and dates of effect for planned price changes.
  • Goods and services paid for through loans (for instance, motor vehicles). For index purposes, the price recorded is the full transaction price of the product at the time of acquiring the product. The method and timing of payment is irrelevant under an acquisitions approach.
  • Goods and services regularly paid for in advance (for instance, international airfares, club membership and magazine subscriptions). For index calculation purposes the price is included when the good or service is actually acquired (i.e. date of the flight for an airline ticket or the commencement date of the subscription period) and not the date at which the payment is made. However, prices are collected at the time payment would normally be made. For example, a ticket for domestic airline travel is typically paid for about a month before the departure date, so the price included in the CPI for a June flight is that price collected in May for travel in four weeks' time.


8.30 As the CPI is compiled on a quarterly basis, prices of most goods and services in the regimen are collected once each quarter. Prices of goods and services that are considered to be volatile (i.e. likely to change more than once during a quarter) are collected more frequently. A small number of items are collected only once a year, either due to known price review periodicity (e.g. council rates) or seasonal availability (e.g. football matches). The general approach is to price each item as frequently as is necessary to ensure that reliable measures of quarterly price change can be calculated. Information about the frequency of collection of the various products in the index is included in the detailed descriptions for each CPI group in this Chapter.

8.31 The following sections describe in more detail the price collection methodology used in each of the 11 CPI groups. A brief description is provided of the group’s index structure, products priced, the frequency of collection and the types of outlets from which the prices are collected. Collection issues specific to each group are also highlighted.

See also:

This section contains the following subsection :
      Communication to Miscellaneous
      Food to Clothing and Footwear
      Housing toTransportation

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