Statistical Office of Slovak Republic (SOSR)

Department of price statistics

Statistical Office of the Slovak Republic

Lamačská 3/C
840 05 Bratislava

Slovak Republic

The harmonised index of consumer prices (HICP) is a consumer price index (CPI) that is calculated according to a harmonised approach. It measures the change over time of the prices of consumer goods and services acquired by households (inflation).

Due to the common methodology, the HICPs of the countries and European aggregates can be directly compared.

European classification of individual consumption according to purpose (ECOICOP)

The HICP covers the final monetary consumption expenditure of the household sector.

The main statistical variables are price indices.

The basic unit of statistical observation are prices for consumer products.

3.6.1. Statistical target population

The target statistical universe is the 'household final monetary consumption expenditure' (HFMCE) on the economic territory of the country by both resident and non-resident households. The household sector to which the definition refers, includes all individuals or groups of individuals irrespective of, in particular, the type of area in which they live, their position in the income distribution and their nationality or residence status. These definitions follow the national accounts concepts in the European System of Accounts.

3.6.2. Coverage error population

HICP covers target population including institutional households.

3.7.1. Geographical coverage

The HICP refers to the economic territory of a country as referred to in paragraph 2.05 of Annex A to ESA 2010, with the exception that the extraterritorial enclaves situated within the boundaries of a Member State or a country are included and the territorial enclaves situated in the rest of the world are excluded.

3.7.2. Coverage error regions

No national specifics.

3.8.1. Start of time series

The HICP series started in January 1997.

3.8.2. Start of time series - national specifics

The Slovak HICP series started in January 1996 and the HICP-CT in December 2002.

See the HICP database

2015=100

The following units are used:

• Index point
• Percentage change on the same period of the previous year (rates);
• Percentage change on the previous period (rates);
• Percentage share of the total (weights).

HICP is a monthly statistics.

Harmonised Indices of Consumer Prices (HICPs) are harmonised inflation figures required under the Treaty on the Functioning of the European Union. Regulation (EU) 2016/792 of the European Parliament and the Council of 11 May 2016 (OJ L 135) sets the legal basis for establishing a harmonised methodology for the compilation of the HICP and the HICP-CT.

This regulation is implemented by Commission Regulation (EU) 2020/1148 of 31 July 2020.

Further documentation, can be found in Eurostat’s website - HICP dedicated section, namely recommendations on specific topics, under the methodology page, and guidelines, under the quality page.

Not available.

Regulation (EC) No 223/2009 of the European Parliament and of the Council, of 11 March 2009, on the transmission of data subject to statistical confidentiality to the Statistical Office of the European Communities.

Protection of confidential statistical data is guaranteed by the Act No 540/2001 Coll. on State Statistics, as amended.

Published indices are calculated from the aggregated individual data - no disclosure is then possible.

In line with the Community legal framework and the European Statistics Code of Practice Eurostat disseminates European statistics on Eurostat's website (see point 10 - 'Accessibility and clarity') respecting professional independence and in an objective, professional and transparent manner in which all users are treated equitably. The detailed arrangements are governed by the Protocol on impartial access to Eurostat data for users.

The HICP is released according to Eurostat’s Release calendar.

The calendar is publically available and published at the end of the year for the full following year.

Release calendar of SO SR

The data are released simultaneously to all interested parties by issuing the Information reports, which is posted on the Internet website of the Statistical Office of the Slovak Republic) at 9:00 a.m. (CET time) on the day of release. Copies are available to the public from the SO SR Press Secretary and from the Information Service of the SO SR.

Monthly

HICP is released on the website of SOSR in Slovak and English language. 

HICP index figures are  disseminated with 2 decimals, HICP rates with 1 decimal

Informative report, HICP indices to the different basis

The HICP are published on the Internet website of Statistical office of the Slovak Republic, usually on the date of release of HICP by Eurostat, but SO SR publishes HICP at 9:00

 Eurostat : HICP database

Statistical office of Slovak Republic database

Microdata can be provided for researches.

Not available.

The HICP Methodological Manual provides the reference methodology for the production of HICP. (https://ec.europa.eu/eurostat/web/products-manuals-and-guidelines/-/KS-GQ-17-015)

10.6.1. Documentation on methodology - national specifics

The general methodology of HICP is available on the website of SO SR, where also the link to Eurostat’s HICP dedicated section is provided.

See Eurostat's Compliance Monitoring Report of 2017 on the web page Quality - Harmonised Indices of Consumer Prices (HICP) (europa.eu) and namely the follow-up Report of 2020

The Statistical office of the Slovak Republic (SOSR) is able to provide Eurostat with information for evaluation of HICP compliance monitoring on the basis of Eurostat request. Statistical Office of the Slovak Republic does not have a special certificate confirming the quality of HICP compilation.

11.1.1. Quality management - Compliance Monitoring

Compliance Monitoring

11.1.2. Quality assurance - national specifics

Controls on the quality of the data

There are more levels of data quality control: by the price collectors in 37 regions and by the staff of Trencin Regional Statistical Office where the central checking of prices as well as a compilation of CPI indices is performed.

If a price deviates by more than 20% from the corresponding price in the previous month, a query is raised by the data input system, for the collector to investigate. Since 8 regional co-ordinators (NUTS 3 level) have only one day or so to receive data from the price collectors, and pass it on to the central level, their responsibility concerns mainly the control for data completeness. After data have been centrally collated/processed in Trencin, various reports are produced.

First, a basic report on monthly price movements: flagging those individual prices differing by more than 20% from the previous corresponding price; of those individual prices differing by more than 20% from the national average; minimum and maximum prices; and noting the number of months since a price last changed. This is accompanied by a report comprising all comments made by collectors in the respective month (it is important mainly for the assessment of replaced products; in case of a replacement price collectors are obliged to provide not only the description of characteristics of the replacement, but also other important information concerning observed prices - there are special codes for different types of information for that purpose). Then there is the first calculation of the preliminary indices for elementary aggregates and for all ECOICOP sub-classes, classes, groups and divisions. Officers in Trencin check the price data collected, and take up any queries raised, contacting either the price collectors, or, sometimes, directly the respective outlet. Quality Adjustment is performed at this stage. In some cases, the consultation with Bratislava Central Statistical Office is needed. After all relevant queries have been resolved, the indices are re-calculated, and the various sub-group indices produced.

11.2.1. Compliance monitoring - last report and main results

The last available compliance or follow-up report can be found in Eurostat's web page Quality - Harmonised Indices of Consumer Prices (HICP)

11.2.2. Quality assessment - national specifics

There are no national specifics in quality assessment.

In addition to being a general measure of inflation, the HICP is also used in the areas of:

• wages, social benefit and contract indexation;
• economic forecasting and analysis;
• measuring specific price trends;
• accounting purposes and deflating other series;
• inflation targeting by central banks;
• cross-country economic comparisons.

The euro area (evolving composition) index is used by the European Central Bank (ECB) as the main indicator for monetary policy management. The ECB and the European Commission's Directorate-General for Economic and Financial Affairs (DG ECFIN) use the HICP for assessing price stability and price convergence required for entry into European Monetary Union.

Other users include: National Central Banks, financial institutions, economic analysts, the media and the public at large.

12.1.1. User Needs - national specifics

National Bank of Slovakia and Ministry of Finance of Slovak Republic are the main users.

There are occasional surveys of SO SR regarding user satisfaction.

Indices for ECOICOP categories are produced with the following exceptions:
ECOICOPCODE DESCRIPTION
01.1.1.5 Pizza and quiche
01.1.2.3 Lamb and goat
01.1.2.5 Other meats
01.1.3.1 Fresh or chilled fish
01.1.3.3 Fresh or chilled seafood
01.1.3.4 Frozen seafood
01.1.6.2 Frozen fruit
01.1.6.4 Preserved fruit and fruit-based products
01.1.7.6 Other tubers and products of tuber vegetables
02.1.1.2 Alcoholic soft drinks
02.1.2.2 Wine from other fruits
02.1.2.3 Fortified wines
02.1.2.4 Wine-based drinks
02.1.3.2 Other alcoholic beer
02.1.3.4 Beer-based drinks
02.2.0.2 Cigars
02.2.0.3 Other tobacco products
04.1.2 Other actual rentals
04.1.2.1 Actual rentals paid by tenants for secondary residences
04.1.2.2 Garage rentals and other rentals paid by tenants
04.3.2.2 Services of electricians
04.3.2.3 Maintenance services for heating systems
04.3.2.5 Services of carpenters
04.4.4.2 Security services
04.5.3 Liquid fuels
05.1.1.9 Other furniture and furnishings
05.1.2.3 Services of laying of fitted carpets and floor coverings
05.1.3 Repair of furniture, furnishings and floor coverings
05.2.0.4 Repair of household textiles
05.3.2.4 Toasters and grills
05.4.0.4 Repair of glassware, tableware and household utensils
05.5.1.2 Repair, leasing and rental of major tools and equipment
05.5.2.3 Repair of non-motorized small tools and miscellaneous accessories
05.6.2.1 Domestic services by paid staff
05.6.2.3 Hire of furniture and furnishings
06.1.3.2 Hearing aids
06.1.3.3 Repair of therapeutic appliances and equipment
06.2.1.2 Specialist practice
06.2.3.1 Services of medical analysis laboratories and X-ray centres
07.1.4 Animal drawn vehicles
07.2.1.3 Accessories for personal transport equipment
07.3.1.2 Passenger transport by underground and tram
07.3.3.1 Domestic flights
07.3.4 Passenger transport by sea and inland waterway
07.3.4.1 Passenger transport by sea
07.3.4.2 Passenger transport by inland waterway
07.3.6.1 Funicular, cable-car and chair-lift transport
07.3.6.9 Other purchased transport services n.e.c.
08.1.0.9 Other postal services
08.2.0.1 Fixed telephone equipment
08.2.0.3 Other equipment of telephone and telefax equipment
08.2.0.4 Repair of telephone or telefax equipment
08.3.0.5 Other information transmission services
09.1.2.2 Accessories for photographic and cinematographic equipment
09.1.2.3 Optical instruments
09.1.4.1 Pre-recorded recording media
09.2.1 Major durables for outdoor recreation
09.2.1.1 Camper vans, caravans and trailers
09.2.1.2 Aeroplanes, microlight aircraft, gliders, hang-gliders and hot-air balloons
09.2.1.3 Boats, outboard motors and fitting out of boats
09.2.1.4 Horses, ponies and accessories
09.2.1.5 Major items for games and sport
09.2.2.2 Major durables for indoor recreation
09.2.3 Maintenance and repair of other major durables for recreation and culture
09.3.2.3 Repair of equipment for sport, camping and open-air recreation
09.3.4.1 Purchase of pets
09.4.2.2 Museums, libraries, zoological gardens
09.4.2.4 Hire of equipment and accessories for culture
09.4.2.9 Other cultural services
09.5.1.4 Binding services and E-book downloads
10.3 Post-secondary non-tertiary education
12.1.2.2 Repair of electric appliances for personal care
12.3.2.3 Repair of other personal effects
12.4.0.4 Counselling
12.5.3.1 Public insurance connected with health
12.5.5 Other insurance
12.6.2.2 Fees and service charges of brokers, investment counsellors

The accuracy of the source data is ensured by adhering to a common methodology for determining prices and data sources for the creation of weighting schemes. Data from National Account data, Household Budget Survey data and external sources are used for weights' creation.

Prices are obtained by price collection by internal SOSR employees in shops and service operations, via the Internet and telephone. The prices of selected representative items are also obtained through central data collection. Sufficient coverage and timeliness are ensured. In the outlets where people buy the most the price collection is assured.

The accuracy of HICP is generally considered to be high.

The exact sampling error is not known. The NSI seeks to reduce sampling errors by updating the sample every year. Prices are monitored throughout the country. For fruits and vegetables, price collectors are instructed in which week of the month they should obtain the prices.

Non-sampling errors are not quantified in HICP.

The prices are collected by NSI staff. For this reason, non-sampling errors can arise in a non-response case only if the selected operation is temporarily closed or the monitored goods are temporarily not located in it.

Regarding such temporary phenomena, updating procedures are integrated in the processing program to prevent biases. If the goods are unavailable for a long time or the outlet is closed for a long time, the price collectors are obliged to replace the particular outlet. Errors that could arise in the process of data processing and calculation of price indices are captured by the data processing program.

The full set of HICPs is published each month according to Eurostat’s Release calendar, usually between 15 and 18 days after the end of the reference month.

Each year, the January release is published at the end of February to allow for the annual update of the weights, both of individual product groups and the relative country weights of Members States in the country group aggregates.

The euro area flash estimate is published on the last working day of the reference month or shortly after that.

Since the March 1997, launch of the HICP release, the HICP for the country groups aggregates has always been published on the dates announced in Eurostat’s Release calendar.

HICPs across Member States aim to be comparable. Any differences at all levels of detail should only reflect differences in price changes or expenditure patterns.

To this end, concepts and methods have been harmonised by means of legislation. HICPs that deviate from these concepts and methods are deemed comparable if they result in an index that is estimated to differ systematically by less than or equal to 0.1 percentage points on average over one year against the previous year (Article 4 of Council and Parliament Regulation (EU) 2016/792).

HICP data are comparable over time. There have been several improvements in methodology since HICP was introduced with the aim of improving reliability and comparability of the HICP. These changes may have introduced breaks in time series. However back calculations under the newer standards were performed when appropriate basic data was available.

Differences between the HICP and national CPI

The difference between CPI and HICP are partially caused by their different coverage; imputed rentals and/or some products related to OOH major maintenance and repairs are excluded from the HICP coverage. 

The HICPs are internally coherent. Higher level aggregations are derived from detailed indices according to well-defined procedures.

Not available

The HICP series, including back data, is revisable under the terms set in Articles 17-20 of Commission Implementing Regulation (EU) 2020/1148.

17.1.1. Data revision - policy - national specifics

There is no obstacle to revise HICP data at national level.

In the year 2005, the HICP index revision was carried out following the correction for mistakes in price updated weights for pharmaceutical products in compliance with the Commission Regulation (EC) No 1921/2001, the affected COICOP categories being 06.1.1, 06 and the overall index.

18.1.1. Weights

The main source of data for weights was the statistics of National accounts: Household final consumption aggregates for 2021. Expenditures were subsequently cleansed of: Consumption of households own production, Goods and services received as wages and salaries in kind, Unrecorded economy and others in order to obtain Household final monetary consumption expenditures. The data were finally adjusted on the basis of quarterly national accounts statistics on household final consumption. Data for the 4th quarter of 2022 have been estimated.

18.1.1.1. Compilation at elementary aggregate level

The source of the weights at the lower level (elementary aggregate level) are Household Budget Survey and some additional administrative and external data sources (for example, information from services suppliers in railway and bus transport, gas, electricity, telecom operators, etc.).

The source of the detailed ECOICOP weights for food and non-alcoholic beverages is scanner data and other information.

Other important information sources to improve details are Regulatory Office for Network Industries, Insurance Association, National bank of the Slovak Republic, retail chains, and others. 

18.1.1.2. Compilation of sub-index weights

The expenditure shares at the 4-digit COICOP level are based on annual National Accounts (NA) data for the year t-2 (2021). These expenditure shares were adjusted to reflect better expenditure shares for the year t-1 (2022) for the category: 09.6.0 Package holidays by the following way:

• The NA data for the first three quarters of the year 2022 were combined with the NA data for the fourth quarter of the year 2021; at the 3-digit COICOP level.  In this way, we obtained preliminary expenditure shares for 2022. We obtained the indicator of the change in expenditure as the ratio of these expenditure shares for the year 2022 and expenditure shares for the year 2021. Using this indicator we compiled new expenditure shares better reflecting the situation in 2022. We used the results of this procedure for the category: 09.6. Package holidays.
•  In the process of the adjustment of the expenditure shares, in some cases, we also took into account some additional information (e.g., the price development in the concrete COICOP category).

ECOICOP adjustment of expenditure:
09.6 - Package holidays: increase by 50 %

18.1.1.3. Compilation of sub-index weights

The reference period for National Accounts data sources for the calculation of weights is the year t-2 and quarterly data for 1st-3rd Q t-1 and 4th Q t-2

18.1.1.4. Weights – plausibility checking

The plausibility checking is not performed.

18.1.1.5. Price updating

The Statistical Office of the Slovak Republic in the creation of the weighting scheme also performs HICP price updating of weights. Price updating of weights is at the level of ECOICOP 5 from the average t-2 to December t-1.

18.1.1.6. Compilation of total household final monetary consumption expenditure

Which data sources are used and which adjustments are made to estimate the total Household Final Monetary Consumption Expenditure (HFMCE) needed to compute the country weight?

The main source of the final country weights are the National accounts data for the first three quarters of the year 2022 and the preliminary NA data for the 4^th quarter 2022

In order to obtain data referring to HFMCE, the following expenditure categories were deducted from ‘Final Consumption Expenditure of Households (FCEH) by consumption purpose’:

1. narcotics (02.3.0.0)

2. imputed rentals for housing (04.2.0.0)

3. games of chance (09.4.3.0)

4. prostitution (12.2.0.0)

5. life insurance (12.5.1.0)

6. FISIM (financial intermediation services, indirectly measured (FISIM) (12.6.1.0)

In addition, net purchases abroad (13.0.0.0), i.e., purchases by resident households outside the economic territory of the country less purchases by non-residential households in the economic territory of the country, was deducted from the total.

To complete the transformation of the data from FCEH to HFMCE two following positions were deducted:

1. income in kind, such as free food for employees in agriculture and final consumption that does not involve monetary transactions (e.g. consumption of own-account production of goods)

2. administrative charges of private pension funds and the like (part of ECOICOP 12.6.2)

At the time when the final country weights were calculated, the preliminary NA data for the 4^th quarter of 2022 were available

18.1.2. Prices

Prices are defined as consumer prices including VAT. The price data is mostly based on the price survey; administrative data sources are used only in specific cases.

18.1.2.1. Data Source - overview  

The principal price data sources are:

• Outlets
• Internet
• Administrative sources
• External organisation

18.1.2.2. Scanner data - general information

SO SR currently receives data on a weekly basis from the 5 largest retail chains in the Slovak Republic. The data is analysed and software for processing this data is under preparation.

For 2023, the scanner data were used to generate the detailed weights for the COICOP 01 - Food and non-alcoholic beverages, and for ECOICOP 02 - Alcoholic beverages and tobacco. The processing of scanner data is managed by the Statistical Surveys and Methodology Department of SO SR.

18.1.2.3. Web scraping - general information

The SO SR does not use web scraping in the HICP.

18.1.3. Sampling

18.1.3.1. Sampling design: locations for survey

Prices are collected within 37 price collection regions in Slovakia, which are spread across the country.

18.1.3.2. Sampling design: outlets

About 9 900 outlets in the country are chosen for the survey. Outlets are selected on the regional level (following the recommendations given in 'Methodological instructions for price collection, verifying and reporting of data on consumer prices'; the outlets where people usually do their shopping are chosen preferably).

18.1.3.3. Sampling design: newly significant goods and services

Price collectors play important role in the process of identifying and introducing new goods and services into the index. Price collectors deal with consumer price survey. During the year they follow the information on the priced goods and services in their field work. On the basis of this information they give the proposals on inclusion of the new representative items, on the changes of the descriptions of the representative items and/or on the cancellation of some representative items. Based on the evaluation of the proposals of price collectors and the data processing teams, the joint meeting of people involved in consumer price statistics is usually held. On the basis of the outcomes of this meeting, decisions are taken on inclusion of newly significant representative items, on changes in their descriptions and/or on exclusion of some representative items. Examples of some newly introduced items:

• 2013: bicycle helmet, USB devise and lawn mower
• 2015: laminate flooring, portable radio with CD/MP3
• 2016: cable headphones, colour multifunctional device, software - operating system, hard disc, game console – Xbox, grilled or baked fish, pasta with meat
• 2017: tablet, bounce vehicle for children, fee for day-care for old and disabled people in special institutions
• 2018: car camera, social hairstyle, private nursery, combined transport, telecommunication services provided in a package, external study fee - 3rd year bachelor study
• 2019: non-alcoholic beer,  humidifier,  dishwasher tablets,  choice of doctor - operator or  obstetrician, physiotherapist: individual therapy, massage, digital camera - slr (camera + lens), adhesive artificial nails with modelling
• 2020: gluten-free long-keeping bread,  lactose-free long-keeping milk, alternative natural sweeteners, girls 'leggings, wood briquettes
• 2021: daily lunch menu delivery, cappuccino,  clothes dryer - e-shop, smart watch - e-shop
• 2022: Tobacco filling, Market rent, Robotic vacuum cleaner, Rental of electric scooters, Mobile internet, Electronic subscriptions for newspapers, Beef steak, Antibacterial hand disinfection gel
• 2023: Technical inspection of the gas boiler, Adblue, Set Top Box

Besides these newly introduced items, the selection of cars and pharmaceutical products are updated on a yearly basis.

External data sources are also important concerning the identification of newly significant goods and services. The information from suppliers of goods/services (e.g., companies engaged in distribution of electricity and gas, passenger railway transport, and others) is annually requested with the aim to keep the sample representative. The communication with the telephone companies regarding the selection of the representative packages, with the Ministry of health regarding pharmaceutical products and/or with importers of cigarettes is also important. New products are identified on annual basis several months before the end of the current year  – they are included in the consumer basket for the next year.

Price data is collected every month.

18.3.1. Price collection surveys

The price collection is organised within 37 'price collection regions' (partially corresponding the previous administrative organization of Slovak Republic to the previous 'districts'). In each of these 37 prices collection regions there are price collectors who in most cases have responsibilities within other statistical surveys (not only price collection). The detailed work of verifying the collected prices as well as of all information concerning prices is done at the computation centre in Trencin (the regional office which has responsibility for the computation of price statistics). The CPI team in Bratislava is in close work contact with the CPI team in Trencin in the process of the monthly compilation of CPI. All important issues (such as changes in methodology, or ad hoc problems concerning the verifying of data) and the publication of CPI work are tackled together, but there are areas in which the responsibility is clearly distinguished.

The price collectors are guided via 'Methodological notes' compiled on a monthly basis by regional statistical Office Trencin (in the case of methodological issues in close cooperation with price statistics department Bratislava). Methodological notes deal with ad hoc questions, such as changes of description of representative items during the year, the timetable of the price collection survey.  The regional coordinators inform the other price collectors on the new requirements. The handbook 'Methodological instructions for price collection, verifying and reporting of data on consumer prices' is available for the regional staff.

18.3.2. Timing of price collection

Price collectors collect prices during the first 20 days of the reference month.

Consumer prices as well as other information related to the collected prices are collected and recorded (using the special software) by price collectors - employees of SO SR in 37 price collection regions of Slovak Republic. The detailed work of verifying of the collected prices as well as of all information concerning consumer prices is done at the computation centre in Regional Statistical Office (RSO) placed in Trencin (within the structure of SOSR each RSO is aimed at a particular area of statistics – RSO Trencin is aimed at price statistics). On the basis of this, RSO Trencin is responsible for processing of consumer prices in entire Slovakia.

The validation process in RSO Trencin consists of the following 4 stages:

A. Indices are compiled directly from edited prices

B. Indices are re-compiled after correction of typed mistakes and/or of other mistakes

C. Indices are re-compiled after Quality Adjustment

D. Indices are re-compiled after imputation of the seasonal products that are outside the season.

18.4.1. Data validation - price data

The price collectors edit prices and also characteristics related to the products.

Information on prices is collected by the price collectors - employees of SOSR. The price collectors edit (record) the prices and also characteristics related to the products and/or information related to the prices using the specially developed software.

The software first enables checking of the prices when entering (typing, editing) of the prices in the electronic devices. If the difference in price for a given product offer in the current and the preceding month is greater than 20 %, the software will display a notification. If it is not a real price increase/decrease, but a  'typo' mistake, the price collector corrects this price using the software. If it is a real price increase/decrease, the price collector has to comment this change. The software also enables to check the completeness of the prices for all representative items – it is possible to check the number of recorded and unrecorded prices for each outlet.

The detailed work of verifying the collected prices as well as of all related information concerning prices is done by the process of the compilation of index of consumer prices. The various reports are produced by software for the purpose of verification of collected prices. First, a basic report on the month´s prices: in this basic report those individual prices differing by more than 20% from the previous corresponding price are marked; also individual prices that differ by more than 20% from the national average are marked. To every individual price a number representing the number of months since a price last changed is attributed. This basic report is accompanied by a report comprising all comments made by collectors in the month (it is important mainly in the assessment of replaced products – in case of a replacement price collectors are obliged to provide the description of characteristics of the replacement, but price collectors are also obliged to write other important information concerning observed prices – there are special codes for different types of information). Then the first calculation is performed to obtain preliminary indices for elementary aggregates and all ECOICOP subclasses, classes, groups and divisions. The queries arisen during the process of validation of prices are consulted with the price collectors or, sometimes, directly with the outlet.  After the resolution of queries the indices are recalculated and the various sub-group etc. indices produced.

18.5.1. Elementary price index formulae

HICP is a Laspeyres-type index. Each price index for an elementary aggregate is calculated as a ratio of arithmetic mean prices.

18.5.2. Aggregation of different data sources

SO SR compiles HICP indices in breakdown by categories in the ECOICOP classification.

HICP in ECOICOP breakdown include in 2021 the following numbers of ECOICOP classification:

• 12 divisions
• 44 groups
• 96 classes
• 221 subclasses - starting with January 2021 - by adding 'rental of electric scooters' into consumer basket the number of covered subclasses increased to 221 - adding: 07.2.4.1 - Hire of garages, parking spaces and personal transport equipment.

There are about 730 representative items in the HICP, in CPI more - mainly due to different treatment of Owner-occupied Housing in CPI

After the validation of prices the indices for the representative items are calculated. The upper level indices (i.e. indices for subclasses, classes, groups and divisions of the ECOICOP classification) are aggregated using the Laspeyres type index.

18.5.3. Chaining, linking and splicing methods

Starting with January 2005 SO SR introduced the compilation of consumer price indices by chaining using December of a previous year as a linking period. Weights for the elementary aggregates are annually revised to ensure that they reflect current expenditure patterns and consumer behaviour. In order to be able to link the old and the new series, an overlap (link) period is needed in which the index has to be calculated using both the old and the new set of weights. SO SR stated December of the previous year to be the link period. The aggregated indices for overall HICP and for COICOP/HICP categories and ECOICOP categories are calculated based on December of the previous year = 100 and then they are linked to the basis of the average of the year 2015 using the indices for December of the previous year based on average of the year 2015=100.

18.5.4. Quality adjustment – Detailed information

The following introduction part regarding the quality adjustment process is given in the Handbook 'Methodological instructions for price collection, verifying and reporting of data on consumer prices': If the price collector replaces a previously priced product offer by a new product offer and if in the price of replacement also the change of quality of the new product offer in comparison with the previously priced product offer is reflected, then the change of quality shall be adjusted from the price development (in the compilation of price index for this product). The process of quality adjustment (QA) is aimed at the fact that consumer price index shall reflect the pure price change not the price change influenced by the change in quality of the priced products. However the quality adjustment is in practice a complex process. A prerequisite for proper quality adjustment and for assessment of quality change are properly filled 'Table comments' by the price collectors in the prescribed structure (maximum 20 characters for 'brand' of the product offer and maximum 80 characters for other important information related to the product offer). Although the software introduced within the grant projects on the implementation of Commission Regulation (EC) No 1334/2007 (repealed and replaced by Commission Implementing Regulation (EU) 1148/2020) on sampling and QA enables the use of explicit QA methods (e.g. the option price method), in practise, in most of the cases the implicit QA methods (bridged overlap) and/or direct price comparison are used. The reason for a rare use of explicit QA is the fact that in practise it is difficult to obtain enough 'explicit' information related to the characteristic of the products needed for evaluation of quality change.

The QA process is done at the central level of the compilation of consumer price indices. As we mentioned above, the properly filled 'table comments' are very important for the assessment of quality change and for the QA. From this point of view, 'The report of Table comments' produced by the software is important. It contains information related to the collected prices in the prescribed structure (maximum 20 characters for 'Brand' and maximum 80 characters for 'Comments' with the other important information related to the collected price). The table comments refer first of all to the prices collected for the new (replacement) product offers and/or to the product offers collected in the new outlets and also to the prices with the month-on-month change greater than 20 %. This report of table comments also serves for the assessment whether the collected price for the replacement product offer had been collected in compliance with the descriptions of the representative items. If not, the price may be excluded from further processing. The QA is done on the basis of evaluation of the information given in the table comments. In most of the cases the implicit QA (bridged overlap) and/or direct price comparison is used. In the cases of bridged overlap, the software calculates the month-on-month price development of the products 'without' quality change and according to this month-on-month movement, the software adjusts the price of December of the previous year for those representative items in which QA was done. Every QA process is documented in the special kind of report related to the process of QA: every month the software developed in Oracle forms produces output report not only concerning source prices data but also the Production (Output) data - aggregated data for the Slovak Republic, average prices and price indices for the individual representative items, as well as for all ECOICOP categories (including the divisions, groups, classes and subclasses) compiled in 4 phases of the compilation of consumer price indices:

1. Production (Output) data compiled from the 'gross-unverified' data
2. Production (Output) data compiled after the correction of 'typo' mistakes in prices
3. Production (Output) data compiled after the process of quality adjustment taking into account the change of quality of priced products
4. Final production (Output) data compiled after the imputation of seasonal goods prices outside the season

The reports on QA are available on monthly basis.

Quality adjustment (QA) issues for Clothing and footwear, Books, CDs and computer games and for Cars:

• Clothing and footwear

In compliance with the standards, the direct price comparison (B method) is used in Quality adjustment for clothing and footwear. The bridged overlap method is used  rarely for QA of clothing and footwear.

• Books, CDs and computer games

In compliance with the standards, the direct price comparison is used for Long-selling markets approach as well as for rapidly-changing markets approach.

• Cars

Regarding QA for new cars: direct price comparison is used most often at present. The option pricing method is used rarely. However the option pricing method was used in the cases where additional equipment of car was provided for 1Eur 'additional' charge or the additional equipment of car was offered as a special bonus free of charge.

SOSR is provided with the prices of second hand cars from external company – specialists at the pricing of cars. They make some QA taking into account the technical stage of the car and the mileage.

18.5.5. Seasonal items

Until 2010, SO SR used for all seasonal items the carry-forwarded last-observed price in all out-of-season months.

SO SR introduced Commission Regulation No. 330/2009 (repealed and replaced by Commission Implementing Regulation (EU) 1148/2020) for the treatment of selected seasonal goods during the 2010 year.

SO SR started to provide indices with modified methodology to Eurostat since January 2011 (All-Seasonal Estimation).

Not applicable.

None.