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Population - Methodology

I. Basic definition (of statistical area of interest)

Population size (population stock, number of inhabitants/residents) at a particular point in time is one of the key data of demographic statistics. It is calculated by the Czech Statistical Office (CZSO) on the basis of the results of a census of population, houses and dwellings, and an annual balance of demographic events, i.e. it is not taken from the basic population register established for public administration. The population stock is always specified by a reference date and territory and is further broken down by sex, age, or marital status.
 

II. Data sources

1.     Censuses of Population, Houses and Dwellings

2.     Statistical surveys

  • Report on marriage entry (Obyv 1-12) – from 2024, only for reporting the marriage where at least one of the fiancés is a foreigner; from 2026, the report also applies to the entry into a partnership of two persons of the same sex (under the Civil Code)
  • Report on birth (Obyv 2-12) – from 2026, only for reporting the birth of a child whose at least one parent is a foreigner
  • Report on death (Obyv 3-12) – from 2024 only for reporting the death of a foreigner
  • Report on divorce (Obyv 4-12) – from 2026, also for reporting the divorce of a partnership (entered into under the Civil Code) or the dissolution of a registered partnership by court decision (entered into under the Registered Partnership Act)

3.     Administrative data sources

  • Basic Population Register and its editing agenda information systems: the Information System of Population Records (also referred to as AISEO) and the Foreigners Information System (also referred to as AISC) through the Census Information System (CENZIS; administered by CZSO) – from 2024 for data on the marriages of two Czech citizens and on the deaths of Czech citizens, and from 2026 for data on the births to parents with Czech citizenship (both parents, or only the mother in cases where the father was not stated)
  • Information System of Population Records – for migration of Czech citizens
  • Foreigners Information System, administered by the Police of the Czech Republic – for migration of foreigners with valid permanent or temporary residence exceeding 90 days (including foreigners granted temporary protection)

III. Statistical population and sample, imputations and estimations of the non-covered part of the population

Data on population and population structures are obtained (balanced) from periodic (approximately once every 10 years) censuses and from data on population change based on statistics on births, deaths, and migration; and for the balance by marital status also from statistics on marriages and divorces.

Given the statutory obligation to both participate in the census and to report and register events into relevant information systems, both data sets (census data and data on demographic events) are considered to be complete (exhaustive). Only data on the population of the Czech Republic are included in the statistics (see Section VI).

Population balance (for population stocks in an intercensal period) is compiled by adding births and immigrants in a reference period to the census results broken down by registered residence (i.e. permanent residence or temporary residence for over 90 days in the case of foreigners) and subtracting deaths and emigrants in the period (all demographic events are in corresponding residence definition to the census results used for population balance). The census is thus the basis for all data on population size and structure for ten years following the census, i.e. starting the year 2021, the population balance is based on the 2021 Census results, population data in 2011–2020 were based on the 2011 Census results, in 2001–2010 on the 2001 Census results, etc.

Population balance, of which the start-year, mid-year, and end-year population stocks are results, is calculated at the level of municipalities, and for the capital city of Prague, down to the level of basic settlement units. The population of higher territorial units (administrative districts of municipalities with authorised municipal authority (AD AMA), administrative districts of municipalities with extended powers (AD MEP), districts, regions, cohesion regions, and the republic) is always obtained by the sum of the populations of the respective municipalities in the given territorial unit.

Age is given in completed years, i.e. represents the age at the last birthday.

The age structure of the population at the beginning or end of the year corresponds to the structure of the population by year of birth. The age structure of the mid-year population is based on the average of the start-year and end-year populations in individual age units, further adjusted so that the sum of the population in individual ages equals the total mid-year population obtained by the population balance as at 1 July.

IV. Overview of main indicators

In terms of the point in time to which the population relates, the following population stocks are specified:

Start-period population: the population of a given area at the beginning of the reference period, which is a calendar year (most commonly), half-year, quarter or month. For a calendar year, the start-period population represents the population as at 1 January, more precisely at midnight from 31 December of the previous year to 1 January of the reference year.

End-period population: the population of a given area at the end of the reference period. For a calendar year, the end-period population represents the population at 24:00 (midnight) as at 31 December of the reference year.

Mid-period population: the population of a given area at the midpoint of the reference period. The mid-year population represents the population of a given area at midnight from 30 June to 1 July of the reference year, as the result of the population balance of a given area from the beginning of the year to the end of June. The mid-period population of a period shorter than one year (in calendar months) represents the average of the mid-month populations in that period, the mid-month population being the average of the population at the beginning and end of that month.

The CZSO regularly publishes the start-period/mid-period/end-period population of all territorial units broken down by sex.

Sex ratio: the ratio of the number of men to the number of women (usually expressed as the number of men per 100 women) in the total population or in individual age units/age groups at the reference time.

Data on the age structure of the start-year/mid-year/end-year population are commonly available for units of age (with the last open age group of 100+ years). They are published in this detail for the administrative districts of municipalities with extended powers (AD MEP) and higher territorial units. The population of municipalities is published broken down into basic age groups 0–14, 15–64, and 65+ years, and in the case of basic settlement districts of Prague into five-year age groups (more detailed data are available on request – see below).

Ageing index: the ratio of the number of persons aged 65 years and over to the number of children aged 0–14 years (usually expressed as the number of elderly persons per 100 children) at the reference time.

Age dependency ratio: the ratio of the number of persons in the age interval approximating the period of economic inactivity (0–19 years and 65 years and over) to the number of persons in the age interval approximating the period of economic activity (20–64 years) at the reference time. The indicator is alternatively calculated with age groups 0–14, 15–64, and 65+ years (more common in the past).

Average (mean) age: the arithmetic average of ages of all individuals in the population (of a given sex or total) living at the reference time.

Median age: the age that divides a given population into two groups of numerically equal size; the number of persons younger than the median age equals the number of persons older than the median age.

At the level of the Czech Republic, the end-year population by sex and age is further disaggregated by marital status (de jure) into categories of single, married, divorced, and widowed. The population balance by marital status is not calculated for the population of lower territorial units; these data are available from the censuses only.

V. Retrospective corrections, revisions, estimation refinement procedure

Data published as provisional are revised during the year by updating all monthly population data from the beginning of the year once every three months when new provisional data are released for the last quarter (i.e. when the next news release Population change, dataset Population of the Czech Republic and monthly time series Population are issued). Data for a reference year are considered to be final after the release (usually in May of the following year) of definitive data on the population and age structure at all territorial levels in that year. The Czech Statistical Office does not revise the final results of demographic statistics retrospectively.

Once every ten years, the population stock is revised on the basis of the results of the last census of population, houses and dwellings. The revision concerns data on population and its structure by sex, age, and marital status from the beginning of the census year (the year in which the census took place), so that the backward population balance is calculated for the period between 1 January and the census date (in cases where the reference date of the census was not set to 31 December).

The population stock as at 1 January of the census year is the starting point for the population balance in the following ten-year intercensal period. That means that the population as at 31 December of the year preceding the census does not equal the population as at 1 January of the census year (while during the intercensal period, this inconsistency can only occur at regional level in the case of territorial changes valid as of the beginning of the year, otherwise the population at the end of the year always equals the population at the beginning of the following year). Another inconsistency resulting from setting a new base for population balance according to the last census results concerns the difference between the size of total increase (sum of natural increase and net migration) and the result of subtraction the population figure as at 31 December of the year preceding the census from the population figure as at 31 December of the census year, since each of the end-year population figures is based on a different census and the total increase in the census year is counted by the subtracting start-year population figure from end-year population figure of the census year.

VI. Comparability

1. Comparability over time

Since 1 May 2004, all data have referred to citizens of the Czech Republic and foreigners with permanent residence in the Czech Republic, third-country nationals with temporary residence in the Czech Republic holding a long-term visa (over 90 days) or a long-term residence permit, nationals of the EU Member States, Norway, Switzerland, Iceland, Liechtenstein and their family members with notified temporary residence in the territory of the Czech Republic, foreigners granted international protection in the Czech Republic, and (from 2022) persons granted temporary protection in the Czech Republic with usual residence in Czechia.

Until 2000, data referred only to the population with permanent residence in the Czech Republic (irrespective of their citizenship). Since 2001, following the 2001 Census of population, houses and dwellings, the data have also included foreigners with a visa for a stay over 90 days and foreigners granted asylum.

The data on demographic events, on which the calculation of the population is based, always respect the legislation effective at the date when the event took place, with the definitions of individual events changing over the years.

The regional breakdowns of the results of demographic statistics in a reference year refer to the territories valid as at 1 January of that year. If a territorial change occurs during the year (as at a date other than 1 January), this change will be reflected in the statistics for the following year for the first time. Thus, data in the time series for a certain territorial unit may not be fully comparable in the case of territorial changes. The time series of the comparable data on the population stocks and population change of individual territorial units (which refer to the same territorial structure for all years of the time series) are presented in the demographic yearbooks of the (different types of) territorial units (Demographic Yearbook of Regions, Demographic Yearbook of Districts, Demographic Yearbook of Towns, Demographic Yearbook of Administrative Districts of Municipalities with Extended Powers, and Demographic Yearbook of Administrative Districts of Municipalities with Authorised Municipal Authority). 

2. Comparability with other outputs

The population figures published by the Czech Statistical Office differ from the (informative) population figures published by the Ministry of the Interior of the Czech Republic. Figures published by the CZSO follow the final results of the last census, which are further annually balanced by the numbers of births and deaths (based on reports sent to the CZSO by registry offices and information from population register), as well as by the numbers of immigrants and emigrants (statistics made by the CZSO from the data of the Ministry of the Interior). The differences between both data sources are therefore objectively necessary.

The 2011 and 2021 Census results refer to the usually resident population. Thus, the population figures published in the framework of census statistics differ (at the national and regional level) from the data annual demographic statistics, for which the registered residence of the resident of the Czech Republic is the reference.

3. International comparability

Data on population and its structure are provided by Member States to Eurostat in accordance with Regulation (EU) No 1260/2013 on European demographic statistics. According to it, Member states shall provide Eurostat with data on their usually resident population at the reference time. However, if the place of usual residence cannot be established, the usual residence can be taken to mean the place of legal or registered residence (applied for data for the Czech Republic). See Population (national level) (demo_pop) (europa.eu) for more details.
 

VII. Seasonal adjustment

Data on population are not subject to seasonal adjustment.
 

VIII. Dissemination

All national outputs are available on the CZSO website Population | Statistics.

The most up-to-date data on the population of the Czech Republic, individual cohesion regions, regions, and districts are published quarterly, as preliminary, in the dataset Population of the Czech Republic, according to publication dates set in Catalogue of Products | Statistics (data for the Czech Republic are also provided in news release Population change and in monthly time series Population).

Final data on the total population by sex as at 1 January of the reference year in the detailed territorial breakdown (for cohesion regions, regions, districts, and AD MEP) down to the level of municipalities are available in May of a given year. On the same date, detailed data on the population disaggregated by sex and age units down to the level of AD MEP are released, available for three reference dates of a year – at the beginning, in the middle, and at the end. The population by sex and age as at 31 December at the national level is further disaggregated by marital status.

Detailed data on the age structure of the population of individual municipalities or specific localities are not published by default, but can be provided on request addressed to Information Services (infoservis@csu.gov.cz), on condition that the CZSO provides data for 5-year age groups for municipalities with the population of fewer than 1,000 people (due to personal data protection), and for municipalities with the population of 1,000 people and over, data on age structure in age units can be provided to users. The last open age group is the category of 90 years and over in both cases.

IX. Additional methodological information and external links

Quality reports

Available at Population - Reports on quality | CZSO.

Legislation

The Czech Statistical Office performs the State Statistical Service on the basis of Act No 89/1995 Sb, on the State Statistical Service. Its scope is defined in § 4, respectively § 7 of this Act.

The territorial breakdown of the Czech Republic follows Constitutional Act No 347/1997 Sb, on the Establishment of Higher Territorial Self-Governing Units (regions), as amended, on the Act No 387/2004 Sb, on Changes in Regions Boundaries, as amended, and on the Act No 51/2020 Sb, on the Territorial Administrative Division of the State, and the Decree No 346/2020 Sb, on the Determination of Administrative Districts of Municipalities with Extended Powers, the Territories of the Districts of the Capital City of Prague, and the assignment of certain municipalities in other districts, as amended. The CZ-NUTS classification and other territorial code lists for the territory of the Czech Republic are also used (see Main territorial code lists for the territory of the Czech Republic and CZ-NUTS classification (in Czech only)).

Additional methodological information

A new population base for the annual population balance from the year of the last census always causes a break in the time series of population stocks, which at the national level usually means a lower number of residents after the census. The main cause is incomplete deregistration when migrating abroad, which concerns both Czech citizens and foreigners. If a person does not report the termination of his or her stay in the Czech Republic to the competent authorities when moving abroad, this event is not recorded in the administrative data source, and consequently in migration statistics of the CZSO (and population balance), since it is based on data from those administrative data sources. Then, in fact emigrated person remains in the annual population figures (and overestimates them) until the new census, when he or she is not enumerated, or (in the case of a foreigner) until the residence permit expires. Also, changes in census methodology and population definition over the years may be behind breaks in time to some extent.

Details on the methodology related to data on vital events and migration are available in Population change.