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Consumers Price Index: September 2014 quarter
Embargoed until 10:45am  –  23 October 2014
Data quality

Period-specific information
This section has information that has changed since the last release.

General information
This section has information that does not generally change between releases.

Period-specific information

Reference period

Prices were collected during the period July to September 2014. Visits by Statistics NZ staff to retail outlets were made during 1–15 August in the seven smallest consumers price index (CPI) regions and during 1–20 August for the five largest CPI regions. Prices for food and non-food groceries were collected each month, usually between the 8th and 17th of the month. Petrol, fresh fruit, and fresh vegetable prices were collected weekly. Quarterly postal survey prices were collected as at 15 August.

Data influencers

Price changes may be influenced by specific events. Factors that affected the September 2014 quarter CPI are listed below.

  • The annual increase of 11.6 percent in cigarette and tobacco prices was influenced by an 11.28 percent rise in excise duty from 1 January 2014.
  • The strong New Zealand dollar has had a downward influence on the retail prices of internationally traded goods, including cars and appliances.
  • Road user charges for private motor cars, administered by the NZ Transport Agency, increased 9.4 percent on 1 July 2014. Transaction fees associated with the purchase of road user charges remained unchanged, which moderated this increase. Petrol excise tax also increased 3 cents per litre on 1 July 2014.
  • Fewer cars now require a six-month warrant of fitness, which we have shown as a price fall in the CPI.

Response rates

Postal

Target: 93 percent
Achieved: 94.1 percent

Field collection

Prices are collected directly from retail outlets by Statistics NZ price collectors.

Sample size

About 100,000 prices were collected from about 2,800 retail outlets and 2,300 other businesses and landlords.

General information

Imputation

Due to unavailability at the time of price collection, on average 1–2 percent of prices (not including seasonal items such as winter clothing) are imputed each quarter. This is often done by carrying forward the previous quarter’s price. Other imputation is done by applying the movements of similar categories of items.

Review of the CPI

Reviews of the CPI are undertaken every three years. The latest review was implemented with the publication of the September 2014 quarter CPI. The review involved reselecting the basket of representative goods and services, updating the new national expenditure weights, and updating regional expenditure weights.

Consumers price index review: 2014 has more information.

Reweighted CPI food group

The food group of the CPI showed no change from the June 2014 quarter to the September 2014 quarter. This compares with a 0.4 percent increase obtained by averaging the food price index (FPI) across the three months within each of the June and September 2014 quarters. This difference of 0.4 of a percentage point compares with smaller differences when CPI basket and weight reviews were implemented in 2011 and 2008.

A number of factors contribute to these differences. They relate to the timing of the introduction of basket and weight changes.

For the 2014 CPI review, basket changes and updated expenditure weights for the June 2014 month were implemented in the monthly FPI for the July 2014 month. FPI movements up to and including the June 2014 month were based on the 2011 basket and weights. By comparison, the 2014 basket and weights were used for all months of the June 2014 quarter for the food group of the CPI.

For example, packaged leaf salad was added to the 2014 basket and now has about 40 percent of the weight previously allocated to lettuce. Lettuce prices rose strongly in May (which contributed to the FPI) and from the June quarter to the September quarter, whereas packaged leaf salad prices were relatively flat in May (which didn't contribute to the FPI) and from the June quarter to the September quarter, which contributed to the lower movement for the CPI food group in the September 2014 quarter than for the FPI.

With the 2014 CPI review, we have also moved to regional weights based on spending in five broad regions. Before the review, we used regional population shares. The FPI used 2011 regional population shares up to and including the June 2014 month, whereas the 2014 regional spending shares were used for all months of the June 2014 quarter for the food group of the CPI. For example, Auckland now has a higher share (35.5 percent) of spending on food than its 2011 population share (33.4 percent), and there was a lower-than-average change for the Auckland food group in the September 2014 quarter (down 0.2 percent).

The reweighted CPI food group provides the best estimate of change in food prices from the June 2014 quarter to the September 2014 quarter. This is because the reweighted CPI food group gives more new information on spending patterns than the FPI during this transitional quarter from the 2011 basket and weights to the 2014 basket and weights.

Impact of GST rise on the CPI

GST rose from 12.5 percent to 15 percent on 1 October 2010. However, the rise in GST was not immediately reflected in the prices of some seasonally available goods and services in the CPI basket. The rise was reflected when prices for these items were next collected. These items make up about 3 percent of expenditure on goods and services in the CPI. Of this 3 percent, nearly half was reflected in the March 2011 quarter CPI, nearly half in the June 2011 quarter, and the remainder was shown in the September 2011 quarter.

The table below shows what the quarterly and annual percentage changes would have been if prices collected for the December 2010, and March, June, and September 2011 quarters had been processed with GST of 12.5 percent for goods and services that are subject to GST. The CPI would have risen 0.4 percent in the September 2011 quarter, and 2.5 percent for the year to the September 2011 quarter.

CPI processed with GST at 12.5 percent
Quarter Percentage change from previous quarter Percentage change from same quarter of previous year Adjusted index number 
Dec 2010 0.5 2.1 1116
Mar 2011 0.8 2.6 1125
Jun 2011 0.9 3.3 1135
Sep 2011 0.4 2.5 1139

 

Care required when using the CPI to adjust monetary values

The CPI is used to adjust monetary values, such as those in legislation and contracts. Care is required when using the CPI to adjust monetary values during the year-long period in which the rise in GST is reflected in the CPI. Some goods and services in the CPI are not subject to GST, some are zero-rated for GST purposes (meaning the applicable rate of GST is zero), and the rise in GST was not immediately reflected for all goods and services in the CPI that are subject to GST.

Special care is required when the monetary values being adjusted exclude GST.

It would not be appropriate to adjust prices or monetary values that exclude GST (but which are subject to GST) by the CPI movement during the period in which the increase in GST is reflected in the CPI. This would mean that the GST increase is counted twice. Another common use of the CPI is to adjust housing rentals. Housing rentals are not subject to GST. Using the CPI to adjust rental values during the period in which the increase in GST is reflected in the CPI would mean that the adjustments would include the overall impact of the GST increase on the CPI. 

Reference population

The reference population of the CPI covers approximately 98 percent of the usually-resident New Zealand population living in permanent dwellings.

Expenditure weights

Expenditure weights give the relative importance of the goods and services in the CPI basket.

Expenditure weights are updated every three years as part of regular CPI reviews. The current set of weights are derived from the 2012/13 Household Economic Survey (HES) and other sources.

CPI weights are based on household spending for the year to June 2013 (the ‘weight reference period’) expressed in June 2014 quarter prices (the ‘price reference period’).

The relative importance of the CPI groups shows that $24.23 of every $100 spent by households on goods and services in the CPI is spent on housing and household utilities, $18.84 is spent on food, and $14.97 is spent on transport.

More information on the relative importance of FPI groups, subgroups, and classes, is in table 9 of this release. 

Collection methods

Prices used in the CPI are collected through three main methods: visiting retail outlets, postal surveys, and the Internet.

Statistics NZ price collectors personally visit over 2,800 different shops in 12 pricing centres throughout the country: Whangarei, Auckland, Hamilton, Tauranga, Napier-Hastings, New Plymouth, Palmerston North, Wellington, Nelson, Christchurch, Dunedin, and Invercargill.

Before 1 July 2014, we also collected CPI prices in Rotorua, Wanganui, and Timaru. However, in line with recommendation 7 of the CPI Advisory Committee 2013, we stopped collecting prices in these three regions, so we could divert the cost of collection towards funding CPI-related initiatives such as household living-costs price indexes and seasonally adjusted analytical CPI series. Price change for these regions will be directly represented by Tauranga, Palmerston North, and Christchurch, respectively.

In addition to prices obtained by price collectors, about 70 different postal surveys are sent out each month, quarter, or year. These surveys are used primarily to collect prices for services, such as electricity and bus fares. The surveys are sent directly to service providers. In some cases, for sampling and collection reasons, these prices are aggregated to the national level or to broad regions such as Auckland, Wellington, Canterbury, rest of North Island, and rest of South Island. Items where movements for the five broad regions are used include: the purchase of second-hand cars; purchase of new housing; and rentals for housing. In these cases, price movements for the five broad regions are used for the corresponding 12 pricing centres.

The types of outlets visited include supermarkets, department stores, and appliance stores. Prices are collected weekly for motor fuels and for fresh fruit and vegetables; monthly for food, non-food groceries, alcoholic beverages, and newspapers; and quarterly for other goods and services.

Postal surveys are sent to service providers who set prices nationally or with little variation according to location, such as prices for telephone homeline rental.

Prices for products and services (such as digital downloads, package holidays, and air fares) are also collected each month or quarter from the Internet.

Pricing frequency

Prices are collected weekly, monthly, quarterly, or annually, depending on the expected frequency of price changes exhibited by the goods or service.

Accuracy of the data

Elementary aggregate formula

Average prices in the CPI are called elementary aggregates. These elementary aggregates are the first level of the index aggregation. Regional elementary aggregates are calculated for each of the 12 pricing centres where price collection supports regional estimation. In other cases, regional elementary aggregates are calculated for five CPI broad regions (Auckland, Wellington, rest of North Island, Canterbury, rest of South Island) or, where prices do not support regional estimation, directly to a national elementary aggregate. Since the 2006 review of the CPI, the geometric mean, or Jevons, formula has been used to calculate the elementary aggregate indexes for items where outlet substitution is possible (eg for groceries and appliances).

The 'ratio of arithmetic mean prices', or Dutot, formula is used for items where outlet substitution is not possible (eg local authority rates), where prices are subsidised and may fall to zero (eg GPs' fees), for fresh fruit and vegetables (as the first stage of aggregation is across both outlets within each region, and across weeks within each month), and where it is not currently practical to adopt the Jevons formula (eg when prices are aggregated directly to a national elementary aggregate, rather than aggregated to a regional level).

Information about the consumers price index has more information on the Jevons and Dutot formulae.

Method of aggregating monthly collected prices from the monthly to the quarterly level 

Prices are collected monthly for the food group and a number of non-food items in the CPI, including electricity, cigarettes and tobacco, alcoholic drinks, and air travel. These prices are averaged over the quarter for inclusion in the CPI.

The method for calculating these averages is to obtain monthly regional average prices for the item by outlet-weighting the prices collected at different outlets within each region. The monthly regional average prices are used to calculate quarterly regional average prices by weighting each monthly regional average price by the number of days in the month in which it was collected. This is called day weighting. All the regions are aggregated to obtain the national quarterly index by weighting together regional price movements from the base (ie June 2014) quarter to the current quarter, using the regional expenditure weights.

Petrol and diesel prices are collected weekly, usually on Fridays. The CPI petrol price index measures price changes of 91 octane petrol and 95/98 octane petrol. Within each CPI region, an average price per 10 litres of each fuel is calculated from the prices surveyed each week from individual service stations. Monthly regional average prices for each fuel are then calculated as simple averages of the averages for the weeks within each month. Quarterly regional average prices for each fuel are then calculated as the day-weighted averages of the averages for the three months within the quarter. Regional price movements from the base (ie June 2014) quarter to the current quarter are then weighted by the regional population-weighted share of the national expenditure weight, to calculate the national petrol and diesel price indexes for the current quarter.

Since petrol and diesel prices are collected either 12 or 13 times within each quarter, a price change that occurs during the quarter is only partly reflected in that quarter, with the remainder being reflected in the following quarter. This is also the case for commodities that are priced monthly, such as cigarettes and tobacco.

Regional expenditure weights

From the September 2014 quarter CPI onwards, regional price change is weighted using regional expenditure weights for the five broad regions (Auckland, Wellington, rest of North Island, Canterbury, and rest of South Island). Regional expenditure weights use expenditure in each region to weight regional price change. This ensures that price change in regions where households spend more per person on a particular item relative to other regions (eg Auckland which has 33.37 percent of the population and a CPI regional expenditure weight of 34.87 percent) has more influence on the combined national price change for that item.

For broad regions with multiple pricing centres (rest of North Island and rest of South Island), we use population shares to allocate the regional expenditure weight to the pricing centres.

Previously, we used national expenditure weights in each of the (then) 15 regional pricing centres, weighted by the centre’s population share. This change was recommended by the 2013 CPI Advisory Committee (recommendation 6) and aligns with international best practice.

We calculated regional expenditure weights as proportions of national expenditure (eg 35.50 percent of food expenditure is in the Auckland region) for each CPI class or section (the lowest published level) using HES regional expenditure. We applied class/section level proportions to the individual items within that class or section (eg the regional proportions for fruit was applied to national expenditure on each fruit item) to derive regional expenditure on each individual item (eg spending on apples in Auckland).

Regional expenditure was then expressed in June 2014 prices for the respective region (eg apple expenditure in Auckland was expressed in June 2014 apple prices collected in Auckland). The group level regional weights were then calculated by aggregating all food expenditure in each broad region.

We publish CPIs for the five broad regions based on regional council area boundaries. These indexes are available from Infoshare.

For the 2014 regional expenditure weights for the five broad regions, see table 7 of this release.

Outlet weights

Outlets are given appropriate weights to reflect their relative importance in terms of household spending.

'On special' prices

Items that are 'on special' are included in the CPI at the price levels observed at the time of price collection. Quantity specials (such as a 15-pack of beer at a cheaper shelf price than the 12-pack) are also taken into account where appropriate (as the price per bottle for the special is lower).

Key concepts

Standard and non-standard series
CPI series that contribute to the hierarchical structure of the overall CPI are known as standard series. For example, the clothing index, combined with the footwear index, contributes to the clothing and footwear index, which in turn contributes to the all groups index. Components of this pyramid-like structure are known as standard index series. In addition, a selection of non-standard series is published in the information release tables, and additional series can be accessed free of charge from Infoshare. Examples of these non-standard series include:

  • all groups CPI less each of the 11 CPI groups
  • all groups CPI plus interest
  • interest.

The CPI is published at the following levels: group, subgroup, and class – all at the national level. Selected sections within the food group are also published. 

Tradable and non-tradable non-standard series
The tradable and non-tradable component series that appear in table 1 allow users to decompose CPI goods and services into two components: one contains goods and services that are imported or in competition with foreign goods, either in domestic or foreign markets tradables); the other contains goods and services that do not face foreign competition (non-tradables).

Movements in the tradables component (tradable inflation) demonstrate how international price movements and exchange rates are affecting consumer prices. The non-tradables component shows how domestic demand and supply conditions are affecting consumer prices.

The June 2014 quarter expenditure weight of the tradables component is 43.59 percent, compared with 44.01 percent in 2011. The June 2014 quarter weight of non-tradables is 56.41 percent, compared with 55.99 percent in 2011.

The June 2014 quarter tradable/non-tradable weights for each group, subgroup, and class are included in table 6 of the Consumers price index review: 2014.

Consumers price index tradable and non-tradable series presents the methodology used to categorise the tradable and non-tradable series.

Trend measures of price-level change
Over the long term, the CPI captures the broad pattern of price change, but can be influenced by one-off events when analysing price change over shorter timeframes (such as a supply disturbance affecting petrol prices). To remove such influences, analytical measures of price change are calculated in an attempt to isolate the more persistent – or underlying – component of general price-level changes. Several analytical measures are constructed to give a good guide to underlying price-level change. These are a range of 'trimmed means' and a range of 'weighted percentiles' including a weighted median. Trimmed means and weighted percentiles are given in table 11 and table 12 of this release.

Trimmed means 
Trimmed means exclude the influence of the largest increases and decreases in the CPI. This is done at the item level of about 700 goods and services in the CPI basket (eg 91 octane petrol or strawberries). The trimmed means progressively remove the influence of the largest increases and decreases. Weighted percentiles highlight the movement of lower-level indexes at points in the distribution of price changes for a particular time period.

Trend measures of price level change has detailed information on the methodology and compilation of trimmed means and weighted medians.

The central and local government charges index, which appears in tables 3.01, 3.02, and 3.03, made up 10.78 percent of the CPI at the June 2014 quarter.

Central and local government charges non-standard series includes items such as:

  • Housing New Zealand and local authority rentals
  • land transfer registration fees
  • local authority rates
  • water supply and part of refuse disposal, electricity
  • prescription charges and oral contraception, general practitioner fees
  • vehicle relicensing fees, road user charges, driver licensing fees
  • postage
  • State and integrated schools, tertiary education, other education
  • cheque duty, and official passports, licences and certificates.

The goods and services component series that appear in tables 3.01, 3.02, and 3.03 allow users to decompose the CPI into its goods and services components, respectively. The goods component made up 60.44 percent, and the services component 39.56 percent at the June 2014 quarter.

The goods component comprises:

  • the food group (except restaurant meals)
  • alcoholic beverages and tobacco group
  • clothing and footwear group (except clothing services)
  • purchase of new housing, property maintenance materials, water supply, and household energy
  • household contents and services group (except repair and hire of household appliances, hire of major tools and equipment, and other household services)
  • medical products, appliances and equipment; dentures
  • purchase of vehicles, vehicle parts and accessories, petrol, other vehicle fuels and lubricants
  • telecommunication equipment
  • recreation and culture group (except recreational and cultural services, accommodation services, and package holidays)
  • miscellaneous goods and services group (except hairdressing and personal grooming services, jewellery and watch repair, insurance, credit services, and other miscellaneous services).

The services component comprises all items not included in the goods component.

Consistency with other periods or datasets

Impact of the Christchurch earthquakes on price collection

There was no material impact on CPI movements from the Christchurch earthquakes in 2010 and 2011.

For goods and services prices collected quarterly from shops in February 2011, collection was completed in all regions before the earthquake. In March, food (and non-food grocery) prices were not collected by Statistics NZ staff in Christchurch city. For Christchurch, price movements for the rest of New Zealand were used to calculate the March 2011 food price index, which represents one-third of the food group in the March 2011 quarter CPI. This approach was also taken for non-food grocery prices for the March month.

For goods and services prices collected quarterly by postal survey (and posted in early February 2011), there were lower-than-usual response rates for Canterbury respondents. The overall response rate for quarterly postal surveys was about 96 percent, compared with about 98 percent over the previous eight quarters. For most parts of the basket, the usual treatment for missing prices in the current quarter is to use the last reported price. With the lower response rate in the March 2011 quarter, there was the potential for the higher level of non-response to slightly flatten the quarterly movement. Therefore, price movements for responding businesses were used to bring the Christchurch response rate up to its usual level.

Statistics NZ began collecting prices again in Christchurch in April 2011.

For goods and services prices collected quarterly from shops for the June 2011 quarter, collection was completed in May. While the June monthly collection of food and non-food grocery prices was put on hold for the remainder of the week following the Monday 13 June earthquakes, pricing was completed on Monday 20 and Tuesday 21 June.

For goods and services prices collected quarterly by postal survey (and posted in early May), the overall response rate for quarterly postal surveys was about 98 percent, which compares well with previous quarters.

By November 2011, when quarterly collection was undertaken, almost all outlets that had not been replaced had reopened.

Index reference period

All CPI indexes have an index reference period of the June 2006 quarter (=1000), except where additional indexes were added in subsequent reviews of the CPI.

Additions to the CPI basket at the June 2008 quarter resulted in the publication of two new indexes at the class level of the New Zealand Household Expenditure Classification (NZHEC). These classes are clothing accessories, and other education. Before the 2008 review, expenditure on goods and services within these two classes was allocated to other apparel and education items, respectively. There was also one new subgroup, for other education. As the two classes and one subgroup were new, they are expressed on the June 2008 quarter (=1000). Similarly, other property related services were added to the CPI in 2011. The other property related services class is expressed on the June 2011 quarter (=1000).

We did not add or discontinue any class or sub-group level series in the CPI as part of the 2014 review. However, the ‘pet-related products’ class was renamed ‘pets and pet-related products’ due to pets being added to the CPI scope.

Reconciling the FPI and food group of the CPI

When comparing the FPI and the food group of the CPI, strictly speaking, the quarterly food group index number is not the average of the relevant three monthly FPI numbers. There are some technical differences between the monthly FPI indexes and quarterly indexes.

Food prices in the consumers price index and food price index has more information.

Treatment of fresh fruit and fresh vegetables – removal of seasonal adjustment

Until the June 2006 quarter, fresh fruit and fresh vegetable items that exhibited a seasonal pattern were adjusted to remove the effect of normal seasonal change. This treatment was used to reduce the influence of normal seasonal price fluctuations. However, the treatment did not completely eliminate the effects of seasonal fluctuations if shifts in seasonal patterns occurred.

From the September 2006 quarter onwards, the CPI incorporates seasonally unadjusted prices for fresh fruit and fresh vegetables. This is in line with a recommendation made by the 2004 CPI Revision Advisory Committee.

The ongoing, fully unadjusted CPI is linked at the June 2006 quarter to the previously published CPI, which is partly seasonally adjusted. As such, annual movements calculated over the annual period encompassing the June 2006 quarter are based on fully unadjusted index numbers for the latest quarter, compared with partly adjusted index numbers for the same quarter of the previous year. However, analytical time series provided annual movements on a fully unadjusted basis during the year-long transition of the official CPI. During this time, annual movements were based on fully unadjusted index numbers for the latest quarter, compared with partly adjusted index numbers for the same quarter of the previous year.

Availability of regional indexes

Indexes are published for five broad regions: Auckland, Wellington, Canterbury (encompasses Christchurch and Timaru until the September 2014 quarter, then Christchurch only), rest of North Island, and rest of South Island. These series are considered to be fit for purpose and do not make significant use of national pricing indicators in their compilation.

Until the June 2006 quarter, indexes were published for 15 regional pricing centres. These series were not considered ‘fit for purpose’, as price movements from national or broad-region price collection were used to compile them. We calculate series for the 12 regional price centres (15 up until the June 2014 quarter) which are available only on request.

Interpreting the data

Rounding of index numbers and calculation of percentage changes

Percentage changes are published to one decimal place and are calculated from index numbers rounded to the nearest index point. For comparisons that cross the index reference period, rounded index numbers (for the later period) should be compared to unrounded index numbers (for the earlier period).

Distribution of item-level index movements table

The distribution of item-level index movements table in this release gives additional information on the distribution of price movements for the current quarter's CPI. The analytical statistics in the table give an indication of how widespread price changes are, and their relative magnitude when compared with previous quarters.

The weighted average price increase and decrease uses unrounded index numbers for the previous and current periods to calculate item-level price movements from the previous period, and these are weighted using previous period expenditure weights. The previous period expenditure weight for an item is calculated by updating base-period expenditure weights, using the price change for the item from the base period to the previous period.

Movements based on unrounded index numbers are used to determine whether items have increased, showed no change, or decreased in price. Previous period expenditure weights are used to indicate the proportion of the expenditure weight that has increased, showed no change, or decreased.

Detailed contribution information tables

Tables 8.01 and 8.02 include supplementary analytical information for group, subgroup, and class contributions to the overall change in the all groups CPI. The contribution information is given as index points, percentage points, and percentage contributions from the previous quarter and from the same quarter of the previous year. These tables are included to provide a broader perspective of the categories contributing to the movement in the all groups CPI. Where there is only one class within a subgroup, the class is omitted to avoid unnecessary duplication.

The index points, percentage points, and percentage contribution information in tables 8.01 and 8.02 is calculated from unrounded index numbers. Percentage changes are calculated from index numbers rounded to the nearest index point (see 'Rounding of index numbers and calculation of percentage changes', above). As such, the sum of each of the group, subgroup, or class percentage point contributions may differ from the overall percentage change in the CPI all groups.

Weighted average retail prices of selected food items

A selection of average retail prices for the current and previous quarter is included in table 5 of this release. The weighted average prices are calculated by applying index movements to weighted average prices for the June 2006 quarter CPI. They are not statistically accurate measures of average transaction price levels, but do provide a reliable indicator of percentage changes in prices.

Determining the effect of a specified change in a lower-level index

As the CPI and FPI were reweighted at the June 2014 quarter, but continue to be published on an index reference period of June 2006 quarter (=1000), the method used to determine the effect that a specified change in a lower-level index would have on a higher-level index to which it contributes has been modified for the September 2014 quarter and subsequent quarters.

The index points effect and percentage contribution on a higher-level index of a specified percentage change in a lower-level index that contributes to the higher-level index can be determined by:

  1. Adjusting the lower-level index for the previous period (In-1,low) by the specified percentage change (PCn,low) to derive the index number for the current period:

     Image, Formula 1.
  2. Calculating the index points effect on the higher-level index of the specified change in the lower-level index:
     
    Image, Formula 2.  
  3. Calculating the percentage change in the higher-level index that would be caused by the specified change in the lower-level index:
     
    Image, Formula 3.  

I : index
n : period n, where n is the September 2014 quarter or a subsequent quarter (CPI), or the July 2014 month or a subsequent month (FPI)
n-1 : period n-1
Jun14 : June 2014 quarter (CPI) or June 2014 month (FPI)
low : lower-level index
high : higher-level index
W : expenditure weight, expressed as a percentage of the all groups (CPI) or group (FPI) index
PC : percentage change
PE : index points effect
low-on-high : lower-level index on higher-level index

Example:
The effect that a 5.0 percent increase in the petrol index (which has a weight of 5.03 percent in the CPI) from the June 2014 quarter to the September 2014 quarter would have on the all groups CPI index can be calculated by:

  1. Increasing the petrol index for the June 2014 quarter by 5.0 percent to derive the index number for the September 2014 quarter:

    Image, Formula 4.  
  2. Calculating the index points effect on the all groups CPI index of the 5.0 percent increase in the petrol index:

    Image, Formula 5.  
  3. Calculating the percentage change in the all groups CPI index that would be caused by a 5.0 percent change in the petrol index:

    Image, Formula 6.  

Timing of published data

The CPI is published 12 working days after the reference quarter.

CPI rolling review of retail outlets

The first cycle of our rolling review of retail outlets (where we collect prices from for the CPI) was completed in January 2014.

Price Index News: July 2012 has more information on the review’s scope.

At the start of the CPI rolling review, the CPI basket items we track at retail outlets were organised into eight review groups. Consumer electronics items were to be reviewed annually, in group 4 and group 8. However, a decision was made to reduce the number of review groups to seven by reviewing consumer electronics items once, in the last group. This is because external data about the characteristics of consumer electronics items was not available at the time the first scheduled review of that group was to start.

Changes actioned in the first seven review groups were: 

During the CPI rolling review, we reviewed the following:

  • outlets visited in groups 1–4 and group 7
  • product specifications of the items priced at the outlets visited in groups 1–7
  • mix of brands tracked at supermarkets (groups 5 and 6), to ensure they continue to reflect market shares.

We also expanded price collection for the following items:

  • CDs and books – to include local and overseas online retailers (group 3)
  • magazines – to include local online retailers (group 3)
  • takeaway pizzas – to collect prices from pizza chain outlets online (group 4)
  • pre-recorded Blu-ray discs, pre-recorded DVDs, tablets, MP3 players, and computer software – to include local online retailers (group 7).

We will begin the next cycle of our rolling review in 2015.

For more information on the review, please contact:

Nick Martelli
Wellington
04 931 4600
info@stats.govt.nz

Relative importance of home ownership and property maintenance

In quality assurance checks for the 2012/13 Household Economic Survey (HES), released in late November 2013, a classification error was found in the housing and household utilities group. For both the 2006/07 and 2009/10 HES years, some expenditure that should have been coded to property alterations, additions, and improvements was instead coded to property maintenance. See Revision note: Household Economic Survey for further details. HES figures for 2006/07 and 2009/10 have been revised. The largest change resulting from these revisions and affecting 2009/10 is that 'property maintenance services' was overstated by about $840 million, and 'services for property alterations, additions, and improvements' was understated by the same amount.

We implemented the current CPI weights, for the June 2011 quarter, in the September 2011 quarter. The 2009/10 HES was our main source of information for the CPI expenditure weight of the property maintenance subgroup and the property alterations, additions, and improvements component of the weight for the home ownership (ie purchase of newly built housing) subgroup.

We looked at how the CPI would have tracked from the September 2011 quarter to the June 2014 quarter if the revised 2009/10 HES figures for property maintenance and for property alterations, additions, and improvements had been used to reweight the CPI subgroups for property maintenance and home ownership. There would not have been a material cumulative effect on either the all groups CPI or the housing and household utilities group.

We have updated the relative importance of the goods and services in the CPI basket, using 2012/13 HES, from the September 2014 quarter CPI release.

More information

More information about the consumers price index is available on our website.

Statistics in this release have been produced in accordance with the Official Statistics System principles and protocols for producers of Tier 1 statistics for quality. They conform to the Statistics NZ Methodological Standard for Reporting of Data Quality.

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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