Accuracy and reliability

Overall accuracy

The statistics are considered a reliable measure of the population, as municipalities themselves report and confirm the aggregated figures. In addition, Statistics Denmark conducts various checks for potential duplicates and other errors that may be overlooked by the municipalities. Upon publication, there are typically minor instances of non-response and measurement errors in reports from some municipalities. However, known errors are usually corrected in subsequent releases and follow-up validations. Overall, with each re-release of previous years' data, the error rate is typically below 1 pct.

The statistics are considered a reliable measure of the population as municipalities report and confirm the aggregated figures themselves. Statistics Denmark also performs checks for duplicates and other errors that municipalities may have missed.

At publication, minor data loss and measurement errors may occur in some municipalities’ reports. Known errors are usually corrected in subsequent releases and validation follow-ups. The error rate for reissued data from previous years typically remains below 1 pct.

Each municipality is asked annually to review and approve the total number of reports to ensure data quality prior to publication. Læsø Municipality reports and validates via Frederikshavn Municipality.

Approval status:

For 2019–2024, all 98 municipalities have approved the reporting, except for 2018, where 94 municipalities have approved. Aalborg, Gribskov, Horsens, and Sønderborg have not approved for 2018. The number of reports is underestimated for Gribskov and Sønderborg.

For 2017, 97 municipalities approved; Aalborg did not approve due to IT issues.

Notes on Changes to Reporting Categories 2024

In January 2024, one notifier category was phased out and two new notifier categories were introduced:

Phased out:

• Notifier type no. 7: Family or personal acquaintance

Introduced:

• Notifier type no. 12: The child or young person themselves
• Notifier type no. 13: Family or personal acquaintance

Sampling error

The sampling error is zero since the statistic's method is complete enumeration.

Non-sampling error

Before 2017, inter-municipal reports resulted in some duplicates.

The relatively large number of reports reduces the risk of overlooking errors in individual cases. The validation process ensures consistency in total figures, although there may be some uncertainty in the distribution between report categories.

The large number of categories for causes for the notifications can lead to both underestimation of the number of causes given and local variation in interpretation, which may weaken the comparability of the data.

Notes for 2024:

Tønder Municipality reported approximately 500 notifications regarding foreigners in 2024, which were not previously included. These cases are distributed over a time period 2015–2022. For some, the reason could not be determined due to incomplete registration. In cooperation with the Ministry of Social Affairs and Housing, Tønder Municipality received a dispensation to register these reports with the following cause category: “Other concerning behavior in the child or young person, e.g. externalizing behavior.”

Næstved and Nyborg municipalities’ data are underestimated by approximately 100 and 60 reports. Greve municipality's data is overestimated by 50 reports respectively.

Causes for these differences include resource challenges in the municipalities and new contact persons’ difficulties extracting data accurately from digital case systems. For all of these cases, the margin of error is about 3 pct. and thus not considered to significantly affect the quality of data.

In 2024, Sønderborg Municipality experienced challenges related to a change in its case management system. As a result, the municipality's reports are underestimated. The exact extent of the underestimation is not specified. Compared to the municipality's average reporting level over the past five years, the number of notifications in 2024 is estimated to be 9% lower than average.

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 statistics are accurate and reliable as they are based on a full population count, and the overall uncertainty is assessed as low. Quality is ensured, among other things, through an annual validation process with the municipalities, but minor fluctuations may occur when previously unapproved data from earlier years are corrected upon re-publication to address data quality issues. Overall, these fluctuations are small—below 1 pct.—making the statistics reliably accurate. This especially applies to municipalities that were unsuccessful in submitting data for a publication but subsequently report correctly for later releases.

The gradual improvement in data quality means that comparisons between the earliest and the most recent years are less precise than comparisons between two consecutive years. This enhanced data quality is primarily due to ongoing improved practices and error checks conducted jointly by the municipalities and Statistics Denmark. Overall, the statistics are comparable over time, taking into account the data cleanup in 2017, which also covers data back to 2015.

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

With each publication, the figures for the two preceding years are revised. For example, in 2025, new data for the reporting year 2024 will be published along with updated figures for 2023 and 2022. These revisions primarily consist of minor corrections for omissions and measurement errors. While the size of revisions is not calculated as an exact average, in recent years they have typically involved no more than 200–300 notifications nationwide—equivalent to a very small share of the total. As a general rule, data is considered final three years after publication.