Monthly sales indices in retail trade, sale of cars, accommodation and food service activities - Methodology (Basic year 2010)

(covering sections G + I excluding CZ-NACE 46) in the CZ-NACE classification (Czech version of the NACE Rev. 2)

I. Basic definition of activities according to the CZ-NACE classification

The scope of economic activities measured by monthly statistical questionnaires results from current regulations of Eurostat for short-term statistics. With regards to the requirements, the short-term statistics of retail trade, sale of cars, accommodation and food service activities provides information on the development of sales in enterprises the principal activity of which is in: wholesale and retail trade and repair of motor vehicles and motorcycles (CZ-NACE 45), retail trade, except of motor vehicles and motorcycles (CZ-NACE 47), accommodation and food service activities (CZ-NACE section I).

II. Data source and definition of the measured indicator

The data source for the calculation of the monthly sales index is “SP 1-12” survey with annexes, which is common for trade, hotels, restaurants, transportation and storage, information and communication, and market services. Aggregate sales from the sale of own products, goods, and services in the respective month are observed. Initial questionnaire, which is sent as an annex to the units included for the first time in the sample contains indicators on principal activity of the reporting unit and on sales in individual months of the preceding year. Sales are reported excluding VAT.
Specimens of statistical questionnaires are available at: http://apl.czso.cz/pll/vykazy/pdf1 (Czech only).

III. Population and sample selection

The population consists of units that are considered to be active, are classified to the aforementioned CZ-NACE activities, and do their business in order to make profit. Reporting units are selected from the Statistical Business Register. Sample strata are defined by the size of the unit (number of employees) and principal activity. The sample is taken for each stratum separately. The sample includes all units with 50+ employees and also the units, of which there is a low number in the stratum. Since 2009, also all units with the annual turnover of CZK 250 million or more have been included in the sample. In other groups of enterprises proportional sampling is used related to the volume of sales known from an administrative data source. The probability of inclusion of a unit into the sample is directly proportional to the contribution of its sales to total sales of all units in the stratum. This is to secure that the units reporting above-the-average sales have more chances to be included in the sample than those with low sales, which are not thereby exposed to unnecessary administrative burden. However, the importance of small enterprises is not undervalued as the products of weights of individual enterprises and their sales are within the strata equal.

The criterion for inclusion of all units into the sample is applied also during the reference year; the population and the sample are thus regularly updated with newly born units, which comply with the criterion.

IV. Description of sales indices calculation

The sales index shows how sales changed (increased or decreased) in the reference period when compared to the comparative basis. Depending on the index type, the comparative basis is either the corresponding period of the previous year (year-on-year index) or the average period of the base year (fixed-base index).
The sales index serves to analyses of the short-term development and possible predictions of the future development in individual CZ-NACE activities.

Calculation of indices:
For each lowest aggregate of CZ-NACE the y-o-y sales indices at current prices are calculated for individual months. For these CZ-NACE categories y-o-y price deflators are used for individual months of current year and for base year price deflators are related to individual months and to the year’s average. Absolute values of monthly sales at current prices for the lowest CZ-NACE aggregates are converted into the price level of the base year using the method of chaining deflators. By the summation of the lowest aggregates of absolute values of sales at constant prices in individual months we get higher CZ-NACE aggregates from which we calculate y-o-y sales indices at constant prices. In the base year it is true that the sum of monthly sales of aggregated CZ-NACE categories at current prices is equal to the sum of their sales at constant prices. For deflation of sales to constant prices, price deflators excluding VAT related to the base year 2010 were used.

Base period:
In 2013, the base period for short-term statistics changed, which is a standard step made every five years and co-ordinated within the European Statistical System.

• The base period for fixed-base indices changed from the average of the year 2005 to the average of 2010.
• New weighting schemes are used that are derived from results of the structural business statistics for the year 2010.
• According to the Eurostat manual on short-term statistics, new weights were used for recalculation of data back to the year 2009, which entails a revision of data for 2009-2012.
• Data for the years 2000-2008 were connected with updated results via conversion bridges by the annual overlap method. It is characteristic for this method that 2009/2008 year-on-year indices for the entire year cumulation remain after the connection the same as at the original data and the course of the series for the years 2000-2008 does not change, i.e. after the connection the year-on-year indices remain unchanged. However, a consequence of the change is that historical series before the year 2009 lose their additivity; it means that they cannot be aggregated by means of the updated weighting scheme.

V. Retroactive corrections, revisions

In accordance with the revision policy of the CZSO, standard revisions are made in the “SP 1-12” survey with the aim to enhance quality of previously published data by inclusion of reports (questionnaires), which were delivered late for the processing and by correction of data that were reported incorrectly. Along with the February data processing, data for January are revised. When necessary, data revisions are carried out along with the processing of the first month that follows the publication of quarterly data, e.g. with the processing of April data, data for January-March are revised. Final data are published following the processing of all months of the reference year, in June of the following year at the latest.

VI. International comparability

The area of short-term statistics in the European Union is regulated by the EU Regulation No. 1158/2005 amending the Regulation 1165/98 on short-terms statistics. Under this Regulation the EU member states are obliged to provide information on turnover in retail trade (at current and constant prices) on monthly basis. The indicator published by the CZSO is internationally comparable in terms of methodology.

VII. Seasonal adjustment

The size of sales during a year in some industries strongly depends on the season (e.g. retail trade in non-specialised stores with food, beverages or tobacco predominating). In order to find out long-term trends but also to be able to compare month-on-month or quarter-on-quarter development, the CZSO produces seasonally adjusted data, in which the part of sales caused by a different number of working days in a month and by seasonal fluctuation is separated from the original “rough“ series, using a mathematical model. After seasonal adjustment not only y-o-y but also m-o-m (q-o-q) development can be compared. When publishing adjusted time series, we have recalculated backwards data for the previous 14 months. Together with a revision for a year, an adjustment model is changed and therefore the entire time series is recalculated.

The TRAMO/SEAT method recommended also by Eurostat is used for seasonal adjustment. The CZSO uses the JDEMETRA+ programme application (version 2.0.0). So-called direct method is applied, in which each aggregation level is adjusted independently.

VIII. Comparability with other surveys in terms of methodology

Results of monthly surveys may differ from results published from quarterly or annual surveys. Monthly data are required (in order to keep publication outputs) in deadlines when enterprises do not have available precise figures for the reference period and thus they are replaced by an informed guess. Moreover, data from quarterly and annual surveys are modified according to the latest administrative data available – during the final processing, which is made two years after the end of the reference year.

IX. Annex: Sales structure

The CZSO sends annex to the “SP1-12” report (questionnaire) to selected retail businesses, namely Sales structure as a source of further information on retail businesses.

The Forms of retail sale annex focuses mainly on the form of sale over the Internet, its volume, and structure of sale of goods. The survey is carried out irregularly among retail businesses (except for fuel stores), in stalls, and on markets.

The Sales structure annex measures differentiation of sales to sales for services and sales for goods (namely for food sale and for non-food goods) in retail businesses with 1 000+ employees in retail sale in non-specialised stores with food, beverages or tobacco predominating (CZ-NACE 4711). A monthly time series of summary data published every month together with news releases for Retail trade is the output. Revisions are made the same as in “SP1-12” standard monthly survey (as described in point V above).

X. Types of released data

Monthly survey results are published:

1) in the Retail trade news release and Services news release
2) in time series on the CZSO web page Time series
3) they are regularly sent to Eurostat databases
4) in other documents on the Internet

XI. Additional methodological information and external links

Eurostat: Data series metadata according to the Council Regulation (EC) No. 1165/98:
Turnover and volume of sales index (C120 serie)
Turnover in services (D120 serie)

Eurostat: EU short-term statistics legislation

Eurostat: EU short-term statistics methodology and manuals

Contact: Ing. Jana Gotvaldová, tel.: 274052691, e-mail: jana.gotvaldova@czso.cz