Towards an Australian Monthly CPI

Released
27/06/2018

By Leigh Merrington, Economic Research Section

Summary

The Consumer Price Index (CPI) provides a general measure of change in the prices of goods and services acquired by Australian households. It is a key indicator for informing monetary policy, with the Reserve Bank of Australia (RBA) having an explicit inflation target to "keep consumer price inflation in the economy to 2-3 per cent, on average, over the medium term" (RBA 2018). The CPI is also used extensively by government, academics and economists for macro-economic analysis, as well as by businesses and the general community in setting wages and the prices of goods and services.

Over the past few years the Australian Bureau of Statistics (ABS) has undertaken a range of activities to enhance the Australian CPI. These activities include: (a) the annual re-weighting of the CPI (ABS 2017a); and (b) the use of new data sources to compile the CPI, namely transactions data and web-scraped data (ABS 2017b). These strategic enhancements to the CPI have addressed most of the significant topics raised by stakeholders during the 2010 review of the CPI and has positioned the ABS to produce a monthly CPI.

While these activities have enhanced the quality of the CPI, they have also lowered the costs, in particular the data collections costs, required to produce the quarterly CPI. As part of the 2010 review of the CPI, the ABS estimated it would cost an additional $15 million per annum to produce a monthly CPI (ABS 2010). The cost to produce a monthly CPI has significantly reduced as a result of the investment made by the ABS to lower the CPI data collection costs over the past three or four years.

The ABS has begun development work on the feasibility of a monthly CPI. This paper outlines the challenges being investigated in the development phase of the project and proposes an implementation plan. User and stakeholder input is being sought to determine the requirements for a monthly CPI and as a basis for broad community consultation.

Feedback and comments can be directed to:

Leigh Merrington
Director
Economic Research Section
P: (02) 6252 6833
E: price.statistics@abs.gov.au

The ABS Privacy Policy outlines how the ABS will handle any personal information that you provide to us.

Background

The Australian CPI is published once every three months for the March, June, September and December quarters, approximately four weeks following the end of the quarter. Australia is one of only two OECD¹ economies (the other is New Zealand), and the only G-20 (Group of Twenty Finance Ministers and Central Bank Governors) country, that does not produce a monthly CPI. 

Australia is also a subscriber to the International Monetary Fund's (IMF) Special Data Dissemination Standards (SDDS), which sets guidelines for the compilation of statistics for those countries which wish to access international capital markets. The standards recommend that the CPI should be produced monthly. Australia has committed to meeting these standards; however, a monthly CPI is one of the few guidelines Australia does not currently meet (IMF 2016).

A major review of the CPI conducted by the ABS in 2010 found that:

There was significant demand for a monthly CPI. The ABS is persuaded there would be a significant benefit from more timely and responsive economic management if a CPI of equivalent quality to the current quarterly index were available monthly. Additional funding will be required to meet the costs involved in compiling a monthly index (ABS 2010).

Since the 2010 review there have been significant enhancements to the CPI that have reduced the costs of producing the CPI. In particular, the use of transactions data and web-scraping data collection techniques² provides high frequency data at a significantly reduced cost to the ABS. These data sources and collection techniques were not available back in 2010.

A monthly CPI would deliver benefits to informing monetary policy, as well as for macro-economic analysis and forecasting, by providing an earlier indication of the trend of inflation and for identifying turning points. In the RBA's submission to the 2010 review it was stated that:

One benefit for the RBA would be the ability to adjust the official cash rate target in response to a more timely indicator of inflationary trends available one month after the reference period rather than the current delay of up to three months. An adjustment of 25 basis points on the cash rate target results in changes of the order of several hundreds of millions of dollars in interest payments by Australian households (ABS 2010). 

This view remains current today, noting recent RBA statements:

At the moment, we need to wait three more months to gain a better understanding as to whether any particular read on inflation is signalling a possible change in trend or is just noise. That is one of the reasons why the RBA has long advocated a shift to monthly calculation of the CPI  (RBA 2017).

Another benefit of a monthly CPI is the ability to produce monthly volume measures of retail trade. This will provide an earlier and more frequent indicator of the strength or weakness of the retail industry and household consumption in general.

With these benefits for policy makers and the Australian community in mind, along with the recent reduction in collection costs, the ABS has begun development work towards producing a monthly CPI. Additional funding will be needed by the ABS to cover the ongoing compilation, analysis and dissemination costs of producing a monthly CPI.

How could a monthly CPI provide a more timely indication of the inflation trend?

A recent example of when a monthly CPI would have proved valuable for users was the March quarter 2016, where the headline CPI recorded a fall of -0.2 per cent, as shown in figure 1. This was the first negative movement for over eight years and was unexpected for many users. It was unclear at the time whether the quarterly movement was the beginning of a trend of falling inflation, or even deflation, or a one-off. What transpired was a period of lower inflation for a period of six months, before rising again. A monthly CPI would have given users an earlier insight into the trend of inflation leading up to and following the March quarter 2016 result.

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Purpose of the CPI

The CPI has many uses; however, its principal purpose is as a macro-economic indicator of household inflation (ABS 2010). The CPI plays a central role in informing monetary policy and the setting of interest rates.³ Figure 2 shows how the RBA's cash rate is strongly correlated with the headline CPI. 

Changes in the cash rate have a direct impact on interest rates. Interest rates play a key role in the Australian economy: from what households receive in the amount of interest on savings or the interest paid on loans; to the amount that businesses and government invest.

While inflation has been relatively low and stable over the past two decades, a monthly CPI would provide an earlier indication of the trend of inflation and possible turning points, such as what occurred during the global financial crisis of 2008-09.

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Monthly outputs

As part of the development phase of the project, the ABS has the opportunity to determine the level of detail for the published monthly outputs, noting that these may be different from the indexes produced quarterly. The level of detail published needs to be balanced against the requirements of users of the CPI and the resources necessary to compile, analyse and disseminate the outputs each month. The ABS is committed to meeting the needs of users, while making efficient use of its resources.

The ABS will continue to publish quarterly outputs to the same level of detail and timing. The structure of the CPI is shown in Figure 3. Along with the headline CPI, the currently published quarterly series is comprised of: 11 Groups; 33 sub-Groups; and 87 Expenditure Classes (ECs), for each capital city, approximately four weeks after the reference period. Maintaining the same quarterly series is important for continuity, particularly for existing indexation arrangements where the CPI is widely used. It is proposed that these quarterly outputs will be published alongside the monthly outputs each March, June, September and December.

    Figure 3 Structure of the CPI

    Figure 3 Structure of the CPI

    Figure 3 Structure of the CPI

    All groups: is the highest level of the index containing all the groups, sub-groups and expenditure classes.

    Groups: is the first level of disaggregation of the CPI. There are 11 groups in the 17th series CPI.

    Sub-groups: are a collection of related expenditure classes. There are 33 sub-groups in the 17th series CPI.

    Expenditure classes: are groups of similar goods or services. They are the lowest level at which indexes are published and weights are fixed. There are 87 expenditure classes in the 17th series CPI.

    Elementary aggregates are the basic building blocks of the CPI. Each elementary aggregate contains several prices for a particular good or service. There are approximately 800 elementary aggregates in each capital city.

    On a monthly basis, the ABS plans to publish All groups, Group, sub-Group and EC levels for the weighted average of the eight capital cities only. Analytical series including the seasonally adjusted CPI, Trimmed mean, Weighted median and the Tradables and Non-tradables series will also be published each month. Capital city measures will continue to be published on a quarterly basis.

    The ABS will consult with users to determine their requirements for a monthly CPI for informing monetary and fiscal policy, macro-economic forecasting, indexation and deflation purposes in the National Accounts. As part of this consultation process, the ABS is seeking feedback from users on whether this level of detail meets your needs for a monthly CPI.

    Producing a monthly CPI

    CPI price collection

    The Australian CPI distinguishes 87 different Expenditure Classes (ECs).  Of the 87 ECs:

    • 28 use high frequency transaction data, representing a weight of 16 per cent of the CPI;
    • a further 14 ECs are currently collected monthly, representing a weight of 27 per cent of the CPI; and
    • 5 ECs only require an annual collection, representing a weight of 8 per cent of the CPI;
       

    The remaining 40 ECs, representing a weight of 49 per cent of the CPI, use a mixture of administrative data, web-scraped data and manually collected data by phone, internet or in-store.

    To minimise the collection costs of a monthly CPI, the development phase of this project will focus on replacing as much manual collection as possible with administrative data or high frequency web-scraped data.

    Sample allocation

    Where administrative data or web-scraped data is not feasible, the monthly CPI collection will continue to be conducted manually through in-store visits, and/or phone and internet collection. This is likely to be the case for some services where the market consists of predominantly small businesses (e.g. restaurant meals, dental services, hairdressing).

    The current approach for these particular ECs is to collect all prices across one particular month of the quarter. For a monthly CPI the options are to: (i) replicate the current collection for each of the three months within the quarter; and (ii) spread the existing collection across the three months of the quarter.  

    The ABS will investigate the use of the second option and how to optimally allocate the manually collected samples. This may involve increasing the size of some of the smaller monthly samples and investigating whether those ECs with less frequent price change require a monthly collection at all.

    Use of web-scraping

    The use of high frequency web-scraped data presents some challenges in how best to incorporate this into the CPI. Two of these challenges are: (i) how to appropriately weight the products within the sample; and (ii) whether the current matched model approach⁴ is optimal where there is a significant amount of product churn (e.g. clothing). 

    The ABS will investigate methods to deal with these challenges.

    Seasonally adjusted measures

    Included in the suite of CPI outputs are seasonally adjusted measures of the All groups (headline) CPI, Group, sub-Group and EC level for the weighted average of eight capital cities. The Weighted median and Trimmed mean measures (often referred to as underlying inflation) are also produced using seasonally adjusted measures (see ABS 2011 for more information). The ABS will continue to publish these important analytical measures as part of a monthly CPI.

    A sufficient time series of at least three years is usually required to develop reliable seasonal adjustment factors. While a monthly time series is available for around half of the ECs, for the other half there is only a quarterly time series currently available. In these cases, monthly seasonal adjustment factors may have to be modelled using a variety of data sources and methods.

    The ABS will investigate how to produce monthly seasonally adjusted CPI measures with a limited time series. The intention will be to publish these measures alongside the CPI when it is first published on a monthly basis.⁵

    ABS and international experience

    As mentioned previously, Australia is one of the few countries that doesn’t currently produce a monthly CPI. Therefore, there are potentially some important lessons that could be learnt from other countries’ experience in the development and ongoing production of a monthly CPI. 

    In addition to this, there may also be some operational lessons from other macro-economic areas of the ABS that produce a monthly series including Labour Force, Retail Trade and International Trade. Central to this is how to utilise resources efficiently for a monthly statistical cycle.

    Implementation of a monthly CPI

    The development phase of the project is expected to take around 12 months. Following the planning and investigation of a monthly CPI, there will be an additional period of 12 months where the monthly price collection is implemented. This enables sufficient time to imbed the monthly collection and conduct a parallel run with the quarterly CPI. It will then ensure that when the monthly CPI is first published, an annual movement will also be available.

    Conclusion

    A monthly CPI would provide a more frequent and earlier insight of turning points in the Australian economy. This will assist in the formation of monetary policy.

    With the availability of new data sources and web-scraping collection techniques, a monthly CPI is much more feasible now than when it was last investigated in 2010.

    The ABS has committed to development work to produce a monthly CPI. Feedback is being sought as part of a consultation process with stakeholders and users to determine their requirements.

    Footnotes

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    1. The Organisation for Economic Co-operation and Development (OECD) is a group of 35 countries where one of its aims is to produce statistics to a common set of standards and quality.
    2. Web-scraping is a technique employed to extract large amounts of data from websites. Prices can be collected as frequently as desired for all products using purpose-built programs that scan the websites of retailers, find the relevant information and store the information in a time series. The process can be run automatically and as frequently as desired (daily / weekly), providing high frequency information (ABS 2017b).
    3. For more information on the role the CPI plays in monetary policy see https://www.rba.gov.au/education/resources/explainers/australias-inflation-target.html
    4. In a matched sample, items that are priced from period to period are identical in all respects.
    5. Monthly seasonally adjusted measures may be considered experimental for approximately two to three years until a long enough monthly time series has been established.

    References

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    ABS 2010 Outcome of the 16th Series Australian Consumer Price Index Review, cat. no. 6469.0, ABS, Canberra.

    ABS 2011 Seasonal Adjustment of Consumer Price Indexes, cat. no. 6401.0.55.003, ABS, Canberra.

    ABS 2017a Information Paper: An Implementation Plan to Annually Re-weight the Australian CPI, cat. no. 6401.0.60.005, ABS, Canberra.

    ABS 2017b The Australian CPI: A Contemporary Measure of Household Inflation, cat. no. 6401.0, September quarter 2017, ABS, Canberra.

    ABS 2017c Information Paper: An Implementation Plan to Maximise the Use of Transactions Data in the CPI, cat. no. 6401.0.60.004, ABS, Canberra. 

    IMF 2016, International Monetary Fund 2016, Annual Observance Report of the Special Data Dissemination Standard for 2016, IMF, Washington D.C.

    RBA 2017, 7th Warren Hogan memorial Lecture by Guy Debelle, Deputy Governor, Reserve Bank of Australia, Sydney, 26 October 2017; available at http://www.rba.gov.au/speeches/2017/sp-dg-2017-10-26.html

    RBA 2018 https://www.rba.gov.au/monetary-policy/

    Frequently asked questions

    The below Frequently Asked Questions are specific to the developmental work and feasibility, conducted by the ABS on a monthly CPI.

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    Will the monthly CPI be the same quality as the quarterly CPI?

    The quality of the monthly CPI will be equivalent to the quarterly CPI.

    For approximately 85-90 per cent of the CPI the same source data will be used in the monthly CPI as the existing quarterly CPI, noting that many Expenditure Classes are collected and compiled monthly now. This includes the use of transactions data, web-scraped data, administrative data and manually collected data (e.g. telephone, in-store) on a monthly basis. Additional data collection, primarily using web-scraping is also expected to occur.

    For the remaining 10-15 per cent of the CPI, development work will assess methods and data sources to produce a high quality monthly CPI. This assessment will examine how to allocate the sample optimally to determine which quarterly samples need to be increased for the monthly CPI or simply spread across the three months of the quarter.

    Will the monthly CPI be more volatile than the quarterly CPI?

    The availability of new data sources such as transactions data and administrative data, and collection techniques, including web-scraping, means greater coverage of products and retail outlets from which to produce a monthly CPI. The ABS now collects around one million prices each quarter for the CPI. This will increase further to produce a monthly CPI. This level of coverage will ensure a monthly CPI does not contain spurious volatility as a result of a more frequent production.

    Consumer prices are relatively dynamic in products such as: automotive fuel; clothing and footwear; fruits and vegetables; and domestic travel airfares and accommodation. A monthly CPI will reflect price change in the same way the quarterly CPI currently does. 

    Currently users are required to wait an additional three months to see whether a particular movement is a one-off, or the beginning of a change in the inflation trend (e.g. the March quarter 2016 quarterly movement of -0.2%). A monthly CPI will provide an earlier and more frequent indication of price change. This is particularly important in informing monetary policy.

    The ABS produces, and will continue to produce, two trend measures to complement headline inflation measures: the Trimmed mean and Weighted median. Figure 3 shows how the trend measures provide an insight into the underlying inflation from a demand point of view. As with the quarterly release, the Weighted median and Trimmed mean will be published on a monthly basis. 

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    Will there be discrepancies between the monthly CPI and the quarterly CPI?

    Consistent with current practice where some components of the CPI are already produced monthly, the quarterly outputs will be derived directly from the monthly outputs. The quarterly price indexes will be calculated by taking the average of the three monthly price indexes. The quarterly movements will be derived from the quarterly indexes. This approach ensures the price index movements are consistent between the monthly and quarterly series, subject to small rounding differences. 

    Table 1 contains a simple example of how the quarterly CPI will be calculated using the monthly indexes.

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    Table 1: Example of how quarterly CPI is calculated
    MonthMonthly IndexQuarterly IndexMonthly movementQuarterly movement
    %%
    January112.0   
    February112.1 0.1 
    March112.6112.20.4 
    April112.6 0.0 
    May113.0 0.4 
    June113.1112.90.10.6

    The quarterly index is calculated by taking the average of the three monthly indexes. For example:

    \(\text{March quarter} = (112.0 + 112.1 + 112.6)/3=112.2\) (rounded to one decimal place)

    What data sources will the monthly CPI use?

    The Australian CPI distinguishes 87 different Expenditure Classes (ECs).  Of the 87 ECs:

    • 28 use high frequency transaction data, representing a weight of 16 per cent of the CPI;
    • 14 are currently collected monthly, representing a weight of 27 per cent of the CPI;
    • 5 only require an annual collection, representing a weight of 8 per cent of the CPI;
       

    The remaining 40 ECs, representing a weight of 49 per cent of the CPI, use a mixture of administrative data, web-scraped data and manually collected data (e.g. phone, internet, in-store).

    To minimise the collection costs of a monthly CPI, the planning phase of this project will focus on reducing as much manual collection as possible and moving the collection to monthly administrative data and high frequency web-scraped data.

    Will the ABS publish CPI analytical series on a monthly basis?

    Included in the quarterly CPI release are a suite of analytical series, these include: seasonally adjusted CPI; Trimmed mean; Weighted median; Tradables; Non-tradables; Goods component; Services component; CPI including deposit and loan facilities (indirect charges); CPI excluding volatile items; and various CPI excluding measures. 

    These analytical series provide useful insights and different perspectives of inflation. The ABS intends to publish these analytical series on a monthly basis.

    Will the monthly CPI be revised?

    The ABS will not change our revision policy in regards to a monthly CPI, which is CPI original indexes are revised only in exceptional circumstances, such as to correct a significant error.

    Will the ABS publish the Selected Living Cost Indexes (ABS cat. no. 6467.0) on a monthly basis?

    The Living Cost Indexes (LCI) have been designed to answer the question: 'By how much would after tax money incomes need to change to allow households to purchase the same quantity of consumer goods and services that they purchased in the base period?'

    The main uses of the LCIs are for indexation purposes for government payments such as the Age Pension. LCIs on a monthly basis are not required for indexation purposes.

    At this point in time, the ABS does not intend to publish the Living Cost Indexes on a monthly basis. Users are invited to provide feedback on this decision.