Reference metadata describe statistical concepts and methodologies used for the collection and generation of data. They provide information on data quality and, since they are strongly content-oriented, assist users in interpreting the data. Reference metadata, unlike structural metadata, can be decoupled from the data.
“Short-term Business Statistics and Statistics of Transport” Department
1.3. Contact name
Confidential because of GDPR
1.4. Contact person function
Confidential because of GDPR
1.5. Contact mail address
2, P. Volov Str.; 1038 Sofia, Bulgaria
1.6. Contact email address
Confidential because of GDPR
1.7. Contact phone number
Confidential because of GDPR
1.8. Contact fax number
Confidential because of GDPR
2.1. Metadata last certified
31 May 2025
2.2. Metadata last posted
31 May 2025
2.3. Metadata last update
31 May 2025
3.1. Data description
Construction Production Indices is an important short-term economic indicator of business, which purpose is to measure the monthly changes of the construction production between two comparable periods. This information can be used to analyze the current state of the construction activity in the country, as well as short-term forecast for its future development.
The main source is the monthly survey ‘Sales in industry, construction, trade and other services’. Data collected with that enquiry are real hours worked from persons employed who are directly engaged in the production process in construction - total and separately by type (building construction, civil engineering and specialized construction activities).
3.2. Classification system
Classification of Economic Activities NACE Rev. 2.
Classification of types of constructions (CC) - the building construction includes construction of residential and no-residential buildings and civil engineering - infrastructure construction of roads, bridges, pipelines, power lines, telecommunication and other construction equipment.
3.3. Coverage - sector
Activities covered:Section F of NACE Rev. 2; Construction - total and separately for building construction and civil engineering, according Classification of types of constructions (CC).
Size classes covered: The survey covers enterprises with 5 or more persons employed in the previous reference year.
3.4. Statistical concepts and definitions
The purpose of Construction Production Indices is to show changes of the production in section Construction - total and separately for building construction, civil engineering and specialized construction activities, calculated on the base of hours worked, directly employed with construction works. Indices are calculated according to the EU Regulations on STS.
The information collected with the Annes of the questionaire Main short-term indicators is ‘Man-hours worked by the employed in construction enterprises’ for previous and for current month:
man-hours worked for total construction
man-hours worked for building construction
man-hours worked for civil engineering
man-hours worked for specialized construction activities.
3.5. Statistical unit
The reporting unit and observation unit is enterprise (Legal unit considered as enterprise).
3.6. Statistical population
The total population includes about 23 000 construction enterprises. The sampling population includes about 6 000 enterprises with more than 4 persons employed of which sample of approximately 2 400 units are surveyed each month. The surveyed enterprises have more than 75% share in the total turnover in construction.
3.7. Reference area
All regions of Bulgaria are covered.
3.8. Coverage - Time
The indices are calculated from January 2015 to the last month of the reference year.
3.9. Base period
Base year is 2021.
Indices, percentage changes (%).
Month.
6.1. Institutional Mandate - legal acts and other agreements
National Legal basis: The Law on Statistics (Article 20) states that all persons that manage or represent legal persons, are obliged to provide the National Statistical Institute and the Bodies of Statistics with reliable data when filling-in forms and questionnaires on surveys included in the National Statistical Programme, for which mandatory participation is provided.
Obligation on units to provide data: The survey is included into the National Statistical Programme – it is compulsory. The Law of statistics includes provisions relating to fines, which can be imposed for refusal, non-response and delay. They are laid down in specific Chapter 9 “Administrative and liability provisions” in article 52.
EU Legislation: Regulation (EU) 2019/2152 of the European Parliament and of the Council on European business statistics, repealing 10 legal acts in the field of business statistics (EBS-Regulation) and Implementing regulation - 2020/1197 - EN - EUR-Lex.
All EU documents following the EBS-Regulation can be found in the STS section on Eurostat’s website under Statistics => Short-term business statistics => Legislation.
6.2. Institutional Mandate - data sharing
Indexes of production in construction are published on the NSI website and the data are available to the users.
According to the EBS Regulation data is transmitted to Eurostat.
Data are sent to other international organizations on request.
7.1. Confidentiality - policy
The National Law on Statistics includes provisions relating to data confidentiality and protection of secrecy, which are in compliance with the EU legislation and standard European practice. In the Law is stated that individual data received and collected at the time of statistical surveys shall be statistical confidentiality and shall be used only for statistical purposes. Individual data, obtained for the purposes of the statistical surveys, shall not be used as evidence to the bodies of the executive powers and the judicial authorities. Requirements, obligations and measures for data protection, as well as fines that can be imposed, are treated in separate chapters, namely Chapter 6 on "Protection of secrecy” and Chapter 9 on "Administrative penal provisions”.
7.2. Confidentiality - data treatment
Article 25 of the Law on Statistics specifies the criteria, according to which certain data cannot be made public or released – individual data, data which could be indirectly identified, as well as aggregations of less than three statistical units and/or when the relative share of one parameter is more than 85% of the total volume of this parameter for all population units.
Data, which according to the Law on statistics are confidential, are not published.
8.1. Release calendar
The date for publication of statistical information is given in the Release Calendar presenting the results of the statistical surveys carried out by the National Statistical Institute, which is available on NSI website. The Indices of production in construction are published 37 - 40 days after the reference month.
Data are simultaneously released to all interested parties. Data are simultaneously posted on the National Statistical Institute website, section Business statistics - Short-term business statistics - Monthly data in accordance with the Law on Statistics and the European Statistics Code of Practice respecting the professional independence and aimed at objectivity, transparency and equal treatment of all consumers.
Indices are also transmitted to various institutes and ministries.
Monthly.
10.1. Dissemination format - News release
Press releases of Indices of Production in Construction are published 37- 40 days after the end of the reference month on the NSI website.
10.2. Dissemination format - Publications
Paper publication -Brochure ‘Bulgaria’
10.3. Dissemination format - online database
Time series with Indices of construction production from January 2015 are available on the NSI website under the heading Statistical data - Business statistics - Short-term business statistics - Monthly data - Construction Production Indices: Statistical data or in the on-line database INFOSTAT.
Indexes are available from January 2015 and include:
The Indexes of production in construction are published as a total for construction (NACE Rev. 2 Section F) and separately for building construction, civil engineering and specialized construction activities. Regional data are neither produced nor published.
10.4. Dissemination format - microdata access
Micro data are neither distributed nor provided to the users.
10.5. Dissemination format - other
Indicators are transmitted to Eurostat at the same time with their national publication.
Data transmission to Eurostat is performed each month. The transmission is carried out in SDMX-ML format via eDAMIS system.
Special tables may be obtained from “Relation with users and e-services“ department of NSI.
Advance notice is given to the public when major changes are introduced in methodology, source of data, base year and statistical techniques.
10.7. Quality management - documentation
The documentation on quality management is available on the Quality.
11.1. Quality assurance
The legal framework which regulates the production of data from Short-term business statistics states that statistical data compiled within the EU system must be of satisfactory quality and produced data are comparable between Member States. Verification of data is done through the process of conducting a statistical survey - from respondents, from experts in the regional statistical offices and from national experts in NSI. Identified inaccuracies and errors are removed timely and comparable data of good quality are provided.
The quality of statistical information and its production process is ensured by the provisions of the European Statistics Code of Practice. The documentation on quality management is available on the Internet: Quality.
11.2. Quality management - assessment
The quality assessment of the Index of production in construction is based on quality requirements of the ESS (relevance, accuracy, timelines and punctuality, accessibility and clarity, coherence and comparability). The monitoring of the quality of the indicator, updating survey methodology, self-assessment of survey manager are carried out. The response rate is about 92 per cent. The coefficient of variation used as the main measure of the accuracy of estimate is about 0.5 per cent.
Index of production in construction are calculated and published at all levels of detail that are required by the EBS Regulation.
13.1. Accuracy - overall
Sampling:
The sampling method used is Stratified Random Sample.
The total population includes about 24 000 construction enterprises. The sampling population includes about 6 000 enterprises with more than 4 persons employed of which sample of approximately 2 400 units are surveyed each month. The surveyed enterprises have more than 75% share in the total turnover in construction.
Criterion for stratification of the enterprises is ‘number of persons employed’. First enterprises are stratified by groups (2-nd digit level of NACE.Rev.2) and then in each group they are stratified by number of persons employed. Enterprises with 30 or more persons employed are surveyed exhaustively. The enterprises with employed from 5 to 14 and from 15 to 29 employed are randomly sampled.
Measurement errors:
The common errors are measurement errors where the respondent misunderstands what information is required or incomplete performance. Most of measurement errors are detected and corrected through the logical and arithmetical controls of the Information system “Short-term statistics” (Online Information system for data collection, editing and processing of the STS information). The system carries out the statutory and warning controls and in a case there are errors, it displays a warning dialog error in the report. The system does not allow completion of the report until they have corrected these errors by statutory controls.
Data processing:
Total Indice of Production in Construction is weighted using the weights from SBS survey for incomes of buiding construction, civil engineering and specialized construction activities for the base year.
Revisions: Every month data is revised so data changes after the first release (data for the current month are published as preliminary and data for the previous month as final). The revisions for the month after the first release did not exceed 0.5 -1.5%.
13.2. Sampling error
Applied sampling method is "stratified random sample" in which first the enterprises stratify by level of activity and then at each level in terms of number of persons employed. To ensure the accuracy of the sample coefficients of variation are calculated also the standard errors which are within acceptable limits.
Coefficient of variation of NACE Rev.2 section F "Construction" is about 0.5%.
13.3. Non-sampling error
The final overall response rate is about 92%.
The size-weighted unit response rate for September 2024 is 0.95.
Actions to reduce the non-response include:
sending the informative reminder letters to the respondents
depending on the relative importance of non-respondents in terms of their size or representativeness in the activity, the postal survey is supplemented by telephone calls and/or direct contact and collection of data for enterprises.
Technical errors:
Technical errors are often recognized with automated checks during the data editing process. A lot of checks are carried out automatically, but under of human interaction. Original data from enterprises for a first time are checking from experts in RSOs. Final checks of data from respondents and the aggregated data analysis are done by responsible experts in Central office of NSI.
14.1. Timeliness
The indices of construction production are published 37 - 40 days after the reference month. Data are provisional when first released. During each reference month, more precise data for the previous month are collected. Each month data for the most recent reference month is produced as preliminary data and data for the previous month is produced as final data.
14.2. Punctuality
NSI fulfils the timeliness requirements of the EBS Regulation. The data are released exactly as planned in the Release calendar. Data are transmitted to Eurostat at the day of the national publication.
15.1. Comparability - geographical
Construction Production Indices are representative for the whole country and have no representation by regions.
The methodology applied for calculation of the index of construction production is in line with international standards, that provides good comparability of the indicators across the countries.
15.2. Comparability - over time
The monthly Indexes of production in construction are presented as time series from January 2015. Indexes are fully comparable over time.
15.3. Coherence - cross domain
Comparisons are made between the rates in the Construction Production Indices and the Production value Indices in Construction from Annual Structural Business Statistics (SBS) survey. Differences between STS Construction Production Indices and SBS Production value Indices in Construction are examined and included in the revisions of Construction Production Indices. Data received from SBS and those receives from STS are coherent.
The existing differences mainly are due to:
Coverage - SBS survey is conducted exhaustively and all enterprises are legally obliged to submit their Annual Reports to the National Statistical Institute. The STS surveys are sampling surveys.
Definition - Annually with SBS survey all elements of ‘production value’ is collected. Monthly for compilation of index of construction production calculated on the base of real hours worked, directly employed with construction works.
Weighting - For compilation the total index of production in construction are weighted using the weights from SBS survey for incomes of buiding construction and civil engineering for the base year.
15.4. Coherence - internal
Data from the monthly statistical survey about hours worked, which is used to calculate the indices of production in construction, are checked with other variable - data for sales (monthly and quarterly) from construction enterprises.
Construction sub-indices for building construction, civil engineering and specialized construction activities are consistent and coherent with total index of construction production (unadjusted and adjusted data).
Since the beginning of 2012 NSI has collected and calculated information online via Information System.
17.1. Data revision - policy
Construction Production Indices usually suffered two revisions. Each month data for the reference month are published as a preliminary and data for the previous month as a final. At the beginning of the year, the indices for the previous year are reconciled on the basis of exhaustive annual data from Structural Business Statistics.
Major revisions are made when there are change of classification, methodology or base year. Users are informed about the results and changes immediately.
This revision policy is applied to STS data relieased nationally and transmitted to Eurostat.
17.2. Data revision - practice
Minor changes are made at the time when the revision is introduced and they are marked in footnotes in the relevant published tables.
The data for the current month are marked as ‘preliminary data’.
Only final data are available on the NSI website.
Major revisions are explained in the methodology and changes in the survey methodology are announced in advance and disseminated at the website.
The regular processes that introduce revisions are for original data series, calendar/working day adjusted data series and seasonal adjusted data series.
The quality indicators, which used in the data revision practice, are:
MAR (Mean Absolute Revision)
MR (Mean Revision)
The computed values for the last 36 monthly of general index (F) Construction are average of the absolute values of the differences between first and latest available release.
The period is January 2022 to December 2024. For calculation, the quality indicators are used indexes:
2022, 2023 and 2024 data first and latest
1.Growth rates for original data series (Y0Y).
MAR=0.16; MR=0.08.
2.Growth rates for calendar/working day adjusted data series (Y0Y).
MAR=0.38; MR=-0.06.
3.Growth rates for seasonal adjusted data series (Y0Y).
MAR=0.49; MR=0.01.
18.1. Source data
The indexes are based on monthly survey “Sales in industry, construction, trade and services” with annex “Hours worked from directly employed in construction enterprises".
Stratified sample survey which frame is based on Register of statistical units.The sample method used is stratified random sampling. Criteria for stratification are the activity and the number of persons employed.There are 24 000 enterprises in the population. Enterprises with 30 or more persons employed are surveyed exhaustively. Enterprises with less than 30 persons employed and 5 or more persons employed are randomly sampled. These enterprises are divided in two strata: from 5 to 14 and 15 to 29 persons employed. Enterprises less than 4 persons employed are not surveyed on a monthly basis. The monthly sample survey includes approximately 2 400 enterprises.
The sample is updated annually.
18.2. Frequency of data collection
Monthly.
18.3. Data collection
The monthly questionnaire ‘Main short-term indicators’ with annex “Hours worked from directly employed in construction enterprises” is used for construction enterprises falling within the population.
Data collection media:
Online through Information system “Business Cycles” (IS BC)
Paper questionnaire. The questionnaires are sent out to the respondents and collected by regional statistical offices, where the information is entered into IS BC.
To reduce non-response Information system “Business Cycles” has functionality to send an informative and a reminder letters to respondents:
automatic formation of electronic letters informing respondents about the upcoming observations, in which they are included. To enable them to attach and reporting forms in PDF format and official letters
provide automatic sending of e-mail reminders to respondents who fail to report the time (when approaching the deadline for submission of reports by the subsystem).
18.4. Data validation
Validation of data in the report:
validation data starts the reports from the filling of by respondents. Control of the data can be accessed from both the regional statistical offices and from experts in the National Statistical Institute. An information system ‘Business Cycles’ significantly contributes to the validation of the data submitted by set of arithmetic and logical controls.
The system carries out the statutory and warning controls. In case there are errors, it displays a warning dialog error in the report. The system does not allow completion of the report while are not corrected the errors. Data validation system incorporates many tools for data control, estimations and detail reports on data completeness. Subsequent analysis of the experts, a phone call for further clarification of data and elimination of disparities, minimize errors in the raw data and ensure accuracy of outputs at national level.
Validation of the output data:
quality checks and data validation is performed during the entire process. Output data are verified at group level with regard to the previous month, with the same month of the previous year and also with regard to extreme values, if necessary data are validated at the level of statistical unit.
Before transmission to Eurostat, the structure of the data file and format is checked in detail.
18.5. Data compilation
Estimates for non-response: Non-response is treated using imputation techniques, depending on specific cases. In the case of non-responding enterprise from exhaustive strata imputation is made for each non-respondent enterprise separately. Non-responses in sampling strata are estimated by adjusting the extrapolation coefficients to take account of response rates.
Estimates for grossing-up to population levels: The grossing up procedure follows the sampling technique. The sample is representative at the 2-digit level of NACE Rev. 2. For enterprises with 5 or more and less than 30 persons employed extrapolation of the results to the population is made using extrapolation coefficients which are based on the number of the units selected and their total number in that particular strata.
The source for activity weights is the mandatory Annual Structural Business Statistics (SBS) survey, which is conducted in accordance with the requirements of EU Regulations on SBS.
18.6. Adjustment
In accordance with EBS Regulation, the Construction Production Indices are to be seasonally and working day adjusted. The software used for seasonally and working day adjustment is JDemetra +v.2.2.2. The method used is TRAMO-SEATS.
Time series the indices of building construction and civil engineering are seasonal and working day adjusted, and time series of the indices of construction - total obtained by applying the indirect method.
Revisions of seasonally and working day adjusted data are published in accordance with accepted revision policy and release calendar for the unadjusted data.
More information about the seasonal adjustment in Annex.
Construction Production Indices is an important short-term economic indicator of business, which purpose is to measure the monthly changes of the construction production between two comparable periods. This information can be used to analyze the current state of the construction activity in the country, as well as short-term forecast for its future development.
The main source is the monthly survey ‘Sales in industry, construction, trade and other services’. Data collected with that enquiry are real hours worked from persons employed who are directly engaged in the production process in construction - total and separately by type (building construction, civil engineering and specialized construction activities).
31 May 2025
The purpose of Construction Production Indices is to show changes of the production in section Construction - total and separately for building construction, civil engineering and specialized construction activities, calculated on the base of hours worked, directly employed with construction works. Indices are calculated according to the EU Regulations on STS.
The information collected with the Annes of the questionaire Main short-term indicators is ‘Man-hours worked by the employed in construction enterprises’ for previous and for current month:
man-hours worked for total construction
man-hours worked for building construction
man-hours worked for civil engineering
man-hours worked for specialized construction activities.
The reporting unit and observation unit is enterprise (Legal unit considered as enterprise).
The total population includes about 23 000 construction enterprises. The sampling population includes about 6 000 enterprises with more than 4 persons employed of which sample of approximately 2 400 units are surveyed each month. The surveyed enterprises have more than 75% share in the total turnover in construction.
All regions of Bulgaria are covered.
Month.
Sampling:
The sampling method used is Stratified Random Sample.
The total population includes about 24 000 construction enterprises. The sampling population includes about 6 000 enterprises with more than 4 persons employed of which sample of approximately 2 400 units are surveyed each month. The surveyed enterprises have more than 75% share in the total turnover in construction.
Criterion for stratification of the enterprises is ‘number of persons employed’. First enterprises are stratified by groups (2-nd digit level of NACE.Rev.2) and then in each group they are stratified by number of persons employed. Enterprises with 30 or more persons employed are surveyed exhaustively. The enterprises with employed from 5 to 14 and from 15 to 29 employed are randomly sampled.
Measurement errors:
The common errors are measurement errors where the respondent misunderstands what information is required or incomplete performance. Most of measurement errors are detected and corrected through the logical and arithmetical controls of the Information system “Short-term statistics” (Online Information system for data collection, editing and processing of the STS information). The system carries out the statutory and warning controls and in a case there are errors, it displays a warning dialog error in the report. The system does not allow completion of the report until they have corrected these errors by statutory controls.
Data processing:
Total Indice of Production in Construction is weighted using the weights from SBS survey for incomes of buiding construction, civil engineering and specialized construction activities for the base year.
Revisions: Every month data is revised so data changes after the first release (data for the current month are published as preliminary and data for the previous month as final). The revisions for the month after the first release did not exceed 0.5 -1.5%.
Indices, percentage changes (%).
Estimates for non-response: Non-response is treated using imputation techniques, depending on specific cases. In the case of non-responding enterprise from exhaustive strata imputation is made for each non-respondent enterprise separately. Non-responses in sampling strata are estimated by adjusting the extrapolation coefficients to take account of response rates.
Estimates for grossing-up to population levels: The grossing up procedure follows the sampling technique. The sample is representative at the 2-digit level of NACE Rev. 2. For enterprises with 5 or more and less than 30 persons employed extrapolation of the results to the population is made using extrapolation coefficients which are based on the number of the units selected and their total number in that particular strata.
The source for activity weights is the mandatory Annual Structural Business Statistics (SBS) survey, which is conducted in accordance with the requirements of EU Regulations on SBS.
The indexes are based on monthly survey “Sales in industry, construction, trade and services” with annex “Hours worked from directly employed in construction enterprises".
Stratified sample survey which frame is based on Register of statistical units.The sample method used is stratified random sampling. Criteria for stratification are the activity and the number of persons employed.There are 24 000 enterprises in the population. Enterprises with 30 or more persons employed are surveyed exhaustively. Enterprises with less than 30 persons employed and 5 or more persons employed are randomly sampled. These enterprises are divided in two strata: from 5 to 14 and 15 to 29 persons employed. Enterprises less than 4 persons employed are not surveyed on a monthly basis. The monthly sample survey includes approximately 2 400 enterprises.
The sample is updated annually.
Monthly.
The indices of construction production are published 37 - 40 days after the reference month. Data are provisional when first released. During each reference month, more precise data for the previous month are collected. Each month data for the most recent reference month is produced as preliminary data and data for the previous month is produced as final data.
Construction Production Indices are representative for the whole country and have no representation by regions.
The methodology applied for calculation of the index of construction production is in line with international standards, that provides good comparability of the indicators across the countries.
The monthly Indexes of production in construction are presented as time series from January 2015. Indexes are fully comparable over time.
