Study design and data sources

We conducted a national mortality follow‐back prevalence study that included all residents in Norway who died from CVD during 2011–2016. The dataset contained information on cardiovascular mortality and complete data on diagnoses and healthcare use in primary care and specialized in‐ and out‐patient settings. Mortality data were obtained from the Norwegian Cause of Death Registry (subsequently referred to as the Cause of Death Registry), diagnostic and health service use data were obtained from the Norwegian Patient Registry (subsequently referred to as the Patient Registry), and data for the for control and payment of health reimbursements in primary care were obtained from the Norwegian Directorate of Health system (the KUHR database, subsequently referred to as the reimbursement database).

The Cause of Death Registry provides almost complete (98%) information on causes of death based on death certificates coded by the physician who examined the deceased 26, supplemented by autopsy data in approximately 8% of the cases. The Patient Registry contains information about all specialized healthcare settings (i.e., government‐owned hospitals and out‐patient clinics, and private health clinics with governmental reimbursement) from 2008. Data from substance abuse treatment facilities were available from 2009. Because of technical problems when reporting data, approximately 15% of publicly funded contacts at private somatic health clinics were missing in the study period 27.

The reimbursement database contains information on all patient contacts with general practitioners (GPs) who receive governmental reimbursement, including visits at the doctor's office or the patient's home, telephone contacts, emergency room visits, and laboratory tests. The reimbursement database is approximately 100% complete, as GPs are mainly funded on a fee‐for‐service basis.

Diagnostic codes in the Cause of Death Registry and the Patient Registry follow the International Classification of Diseases and Related Health Problems, 10^th Revision (ICD‐10), while diagnostic codes for primary care contacts follow the International Classification of Primary Care, 2^nd edition (ICPC‐2). Accurate linkage across registries was obtained using an encrypted personal identification number included in all registries.