Accuracy and reliability

Overall accuracy

The National Patient Register is based upon reports from the individual wards.

With LPR3's introduction in 2019, the National Patient Register became contact-based, so that all contacts with the hospital system are registered and admissions must be calculated via linkage of individual hospital contacts. Despite this change in registration practice and calculation methodology from 2018 to 2019, the actual reporting of contacts is assessed to be high and accurate. Any challenges with or lack of registration must be assumed to have occurred especially close to the transition from LPR2 to LPR3. The Capital Region (Hovedstaden), Region Zealand and Region Midt transferred to LPR3 on the 2nd and 3rd. February 2019. Region South and Region North Jutland switched to LPR3 on 2-3 March 2019. 2019 cannot therefore be compared directly with 2020 and 2021, as 2019 does not contain LPR3 data regarding every 12 calendar months.

Before 2019, data on an admission was reported to the National Hospital Discharge Register when the hospitalization was terminated. This is estimated to have happen in close to a 100 percent of the cases.

An evaluation has been made of the data quality in the National Hospital Discharge Register for 1990. The result of this evaluation is that the administrative data (e.g. dates) in the register is very reliable whereas the medical data (diagnoses) has a lower level of reliability. However, since Statistics Denmark uses the diagnosis codes on an aggregate level, this is not considered to be of great importance. For an evaluation of the reliability of the other registers operated by Statistics Denmark and included in the Hospitalisation statistics, please see the description of these.

In 2016 one region (Hovedstaden) experienced challenges due to implementing a new registration platform in some hospitals. These challenges were solved prior to the transmission of data to Statistics Denmark.

Sampling error

Not relevant for these statistics.

Non-sampling error

The registration of diagnoses may involve some uncertainty at a more detailed level. At the level on which the statistics are published, it is not considered to be a source of uncertainty. In some cases, in previous years in particular, a termination date may be missing for outpatient contacts.

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 National Patient Register is based on reports from the individual wards. The following caveats, which can conceivably influence the overall quality assessment, are known:

With LPR3's introduction in 2019, the National Patient Register became contact-based, so that all contacts with the hospital system are registered and admissions must be calculated via linkage of individual hospital contacts. Despite this change in registration practice and calculation methodology from 2018 to 2019, the actual reporting of contacts is assessed to be high and accurate. Any challenges with or lack of registration must be assumed to have occurred especially close to the transition from LPR2 to LPR3. The Capital Region (Hovedstaden), Region Zealand and Region Midt transferred to LPR3 on the 2nd and 3rd. February 2019. Region South and Region North Jutland switched to LPR3 on 2-3 March 2019. 2019 cannot therefore be compared directly with 2020 and 2021, as 2019 does not contain LPR3 data regarding every 12 calendar months.

Before 2019, data on an admission must be reported to the National Patient Register when the hospitalization is terminated. This is estimated to happen in close to 100 percent of the cases.

The time at which the extract from the National Patient Register is generated for Statistics Denmark may impact the contents. The register is updated continuously by the Danish Health Data Agency.

Up to and including 2011, Statens Serum Institut (SSI) made cleansed versions of the National Patient Register (the so-called “årsbånd” (annual tapes)), and it was this cleansed version (free from e.g. a number of service departments and psychiatric research units in order to ensure that it contained only clinical departments) which Statistics Denmark received.

From 2012, Statistics Denmark performs a form of cleansing where non-clinical departments are disregarded. Cleansing of the National Patient Register ensures continuity in time series.

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

Only final figures are published.