Table S1.

Important changes in health registries

	Danish National Patient Registry	Danish Registry of Causes of Death	Danish National Pathology Registry
Contents	Administrative and clinical information for all hospital contacts, including dates, diagnosis codes, and performed procedures. Diagnoses are registered by the physician discharging the patient. Procedures are registered by the responsible surgeon.	Time and cause(s) of death for every Danish decedent. Cause(s) of death are registered by the physician with most accurate knowledge of patient either hospital physician or practitioner. If autopsy is performed, the pathologist adds his or her findings.	Information on pathological examinations including tests performed, free text description of examination and SNOMED codes on topography and diagnostic conclusions. Data are reported by requisitioning department and pathologist(s) performing examination.
Coverage	Somatic hospital admissions discharged after January 1, 1977, psychiatric admissions discharged after January 1, 1995, and still-active admissions from 2015, and onward. Outpatient contacts ending in or active since 1995. Emergency department contacts since 1995.	Danish residents dying while residing in Denmark since 1970. Danish residents dying in Greenland and the Faroe Islands and Greenlanders and Faroese living in Denmark were included in 1983.	Includes incomplete data from some public pathology departments back to 1970 with national coverage from 1997. Registration became mandatory for private practicing pathologist in 2005.
Important changes in data	Diagnoses registered using Danish adaptions of ICD-8 1977–1993 and ICD-10 1994–now. Changes in registration of surgical procedures in 1981, 1989, and 1996, currently using Danish adaptation of Nordic Classification of Surgical Procedures. Has been basis for reimbursing departments and hospitals since 2000.	Diagnoses registered using Danish adaptions of ICD-8 1977–1993 and ICD-10 1994–now. Data were submitted by paper death certificates in 1970–2006 and electronically since 2007. In the 1970s, 75% of patients dying at hospitals were autopsied compared to less than 20% today.13	Data were submitted by different computer-based systems and with varying data recorded 1970–1996. In 1997 a national standard for which data to register were defined. In 1999 a single national online tool for registering data were introduced.

Note: Data from references 9 and 13 to 16.

Abbreviations: ICD-8, International Classification of Diseases 8th edition; ICD-10, International Classification of Disease 10th edition; SNOMED, Systematized Nomenclature of Medicine.