Based on the DCRS it is possible to construct nationwide cohorts (the current population is approximately 5.5 million) with individual-level and longitudinal information obtained from other national registries such as the National Hospital Discharge Register (NHDR). The NHDR was established in 1977 and contains information on all hospital contacts (diagnoses, operations, procedures) in Denmark11. ICD-8 was used in the period 1977 to 2003. Since 1994, ICD-10 has been used for the coding of discharge diagnoses. Since 1995, the register has included information on emergency department contacts and outpatients – only inpatients were included before.
Data are obtained from the Danish National Board of Health and are available for specific research projects after approval by the Danish Data Protection Agency and the National Board of Health. No ethics approval is needed for the use of register data for research purposes.
 

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