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Accuracy and reliability

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Population and Education, Social Statistics
Annika Klintefelt
+45 39 17 36 78

akf@dst.dk

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Population Projections

The uncertainty concerning the future number of live births, deaths, immigration and emigration - as a result of unexpected changes in the assumptions of the projection about fertility, mortality and migration - must be considered as giving rise to the most significant deviations between the projection and the actual development.

The population projection is deterministic and not stochastic. There is only one scenario and probabilities on different outcomes are not calculated.

Overall accuracy

Projections are subject to some uncertainty. The goal of the projection is primarily to give an idea of how the population will evolve given a number of assumptions. Whether these assumptions are in line with the actual development is uncertain. The uncertainty mainly concerns future immigration of foreign citizens and the proportion of the population which has not been born at the beginning of the projection period. This means that the uncertainty of the projection increases with time as a larger proportion of the population is made up of persons who have not been born at the start of the projection period.

The largest uncertainty attaches to the young age groups, i.e. those who have not been born at the start of the projection period. The size of the population in the oldest age groups is also subject to some uncertainty.

The uncertainty of immigration of foreign nationals is the largest uncertainty in the projection for the whole of Denmark. The largest uncertainty in the regional projection is the number of persons moving to the region from both other parts of Denmark and from outside of Denmark.

It is assumed in the regional projection that the current pattern based on historical data for the past four years will remain throughout the projection period.

The projections are deterministic, that is, based on historical experience. The projection includes only one scenario for future developments. Uncertainty is an important factor, but the uncertainty is not calculated and is also not possible to calculate in the current projection model.

The future number of live births is to a considerable extent decided by the presumed development of the fertility. This means that this variable is subject to considerably uncertainty due to the unpredictability of the future development in fertility. This affects, for example, the number of children in preschool-ages six years into the horizon.

The future number of deaths is subject to some uncertainty. For a long time there has been a clear falling trend in mortality. Mortality is therefore considered somewhat easier to project compared to fertility and migration. Deviations in this component affect mainly the elderly population.

Immigration is subject to considerable uncertainty due to considerable fluctuations and the unpredictability of migrations. It is particularly immigration for non-Nationals that is difficult to predict. Conditions within Denmark and outside of Denmark will affect the number of persons that immigrates.

Emigration is subject to some uncertainty due to considerable fluctuations and the unpredictability of migrations. The uncertainty of emigration is also due to uncertainty about future immigration. Many immigrants emigrate relatively soon after their arrival. A high number of immigrants will therefore also result in a high number of emigrants.

The uncertainty about migration between municipalities in Denmark is important. The number of persons moving to or from a municipality is affected by job opportunities, housing supply and economy. If the projection for Denmark as a whole is under- or overestimated, this will affect the local projections, so that these also are under- or overestimated. Particularly in 2015 this was the case when the number of refugees was underestimated. Because the regional projection model uses an average of four years, it will not reflect a trend. If a municipality has a sharply rising or falling population, the model will even out this development. Since the projection should go about 25 years ahead, it is fair to use a more conservative approach compared to the population growth /reduction.

The municipal projection is "mechanical" in the sense that it does not involve factors that are beyond the purely demographic conditions. The demographic consequences of the decision of increased building of housing are as an example not included. Statistics Denmark's population projection has the very important restriction that the sum of municipalities must sum to the projection for the whole of Denmark. It is not possible to add population into one municipality, without removing the same number from another municipality.

Sampling error

Not relevant for these statistics.

Non-sampling error

The projection's purpose is to give some estimates for the future population. An exercise that is by nature filled with uncertainty.

If the actual development differs from the assumptions in the model, which it definitely will to some extent, the future population will also differ from the population in the projection.

Assumptions for the 2022-projection for the entire country:

Total Fertility

Long term fertility levels for all groups of origin are assumed. They are as follows:

  • Danish origin - Danish citizenship: 1.90
  • Danish origin - foreign citizenship: 1.90
  • Immigrants non-Western countries - Danish citizenship: 1.70
  • Immigrants non-Western countries - foreign citizenship: 1.96
  • Immigrants Western countries - Danish citizenship: 1.73
  • Immigrants Western countries - foreign citizenship: 1.76
  • Descendants from non-Western countries - Danish citizenship: 1.90
  • Descendants from non-Western countries - foreign citizenship: 1.90
  • Descendants from Western countries - Danish citizenship: 1.75
  • Descendants from Western countries - foreign citizenship: 1.75

Origin at birth:

Some of the children born by immigrant- and descendant women will belong to the group of persons with Danish origin, because one of the parents belongs to this group. Therefore, the so-called frequencies of change have been calculated for immigrants and descendants based on the period 2019-2021. The following frequencies state the percentage of new-borns from the groups of immigrants and descendants, that will be classified in the group of persons with Danish origin.

  • Danish origin - Danish citizenship: 100
  • Danish origin - foreign citizenship: 100
  • Immigrants from non-Western countries - Danish citizenship: 20.8
  • Immigrants from non-Western countries - foreign citizenship: 17.4
  • Immigrants from Western countries - Danish citizenship: 48.3
  • Immigrants from Western countries - foreign citizenship: 22.9
  • Descendants from non-Western countries - Danish citizenship: 100
  • Descendants from non-Western countries - foreign citizenship: 34.3
  • Descendants from Western countries - Danish citizenship: 100
  • Descendants from Western countries - foreign citizenship: 36.2

Mortality

Mortality rates are projected using a variant of the Lee Carter method. In 2059 the life expectancy at birth is projected to be 86.9 for men and 89.3 for women. The same assumptions for mortality have been used for all groups of origin.

Immigration:

Immigration rates are used in the entire projection period regarding immigration for persons with Danish origin, descendants and immigrants with Danish citizenship.

Emigration:

Emigration rates are used in the entire projection period for all groups of origin.

Assumptions for the 2022-projection for the 11 provinces:

Fertility:

Fertility rates are calculated for all 11 provinces based on data for the period 2018-2021. Future developments in fertility are given by the national projection, and geographical differences from the starting point are upheld throughout the projection period via an adjustment procedure.

Deaths:

Mortality rates are calculated for all 11 provinces based on latest available data (2017/2021). Future developments in mortality are given by the national projection, and geographical differences from the starting point are upheld throughout the projection period via an adjustment procedure.

Migration out of the province:

Rates are calculated for all 11 provinces based on data for the period 2018-2021. Rates are assumed to be the same in the entire projection period.

Migration into the province:

The estimated number of refugees in 2021 and 2022 is allocated on the basis of regional Allocation of Refugees.

Other persons moving to a region is calculated from the regions share of other in migrations in the period 2017-2020. The number of persons moving to a region is not distinguished by the number from within Denmark and immigrations.

Fertility:

Fertility rates are calculated for all 98 municipalities based on data for the period 2018-2021. They are subsequently smoothed keeping total fertility for the municipality at the same level. Future developments in fertility are given by the national projection, and geographical differences from the starting point are upheld throughout the projection period via an adjustment procedure.

Deaths:

Mortality rates are not calculated at the municipal level. It is assumed that every municipality has the same mortality rates as the province it is a part of.

Migration out of the municipality:

Rates are calculated for all 98 municipalities based on data for the period 2018-2021. Rates are assumed to be the same in the entire projection period.

Migration into the municipality:

The estimated number of refugees in 2021 and 2022 is allocated on the basis of regional Allocation of Refugees.

Other persons moving to a municipalities is calculated from the municipalities share of other in migrations in the period 2018-2021.

Quality management

Statistics Denmark follows the recommendations on organisation and management of quality given in the Code of Practice for European Statistics (CoP) and the implementation guidelines given in the Quality Assurance Framework of the European Statistical System (QAF). A Working Group on Quality and a central quality assurance function have been established to continuously carry through control of products and processes.

Quality assurance

Statistics Denmark follows the principles in the Code of Practice for European Statistics (CoP) and uses the Quality Assurance Framework of the European Statistical System (QAF) for the implementation of the principles. This involves continuous decentralized and central control of products and processes based on documentation following international standards. The central quality assurance function reports to the Working Group on Quality. Reports include suggestions for improvement that are assessed, decided and subsequently implemented.

Quality assessment

The main purpose of the projection is to show how the population will develop given the jump-off population and a set of assumptions. Whether these assumption will be in accordance with the actual development is of course uncertain. The uncertainty is higher the further ahead in the future the projected year is.

In the projection for the entire country uncertainty about future immigration of foreign citizens and future levels of fertility are most important to be aware of.

Regarding the projections on provinces and municipalities it is in particular uncertainty about internal migration one should be aware of. It is assumed in the projections that the current internal migration pattern based on data for the last four years will remain at the same level throughout the projection period.

The projections are deterministic and thus only have one scenario for the future development. Uncertainty is however an important factor, but uncertainty is not calculated and it is not possible to calculate with the current projection models.

Data revision - policy

Statistics Denmark revises published figures in accordance with the Revision Policy for Statistics Denmark. The common procedures and principles of the Revision Policy are for some statistics supplemented by a specific revision practice.

Data revision practice

The published figures are definitive for the projection of the year concerned.