Table 2

Examples of enrichment that can be enabled via linkages of the clinical rheumatology registers to other national and population-based registers

	Sweden	Denmark	Norway	Finland	Iceland
Population (million)	10.1	5.7	5.6	5.5	0.3
Conditions for register linkages
Individual informed consent	Generally not for register-only studies	Not for epidemiological research	Depending on Ethics Review Board assessment of individual projects	Not for register studies by permission from the National Institute for Health and Welfare ad 2020	Not for epidemiological research
Approvals	Ethics Review Board, approval from each register holder	Approval from the data protection agency and from registry holder	Ethics Review Board, approval from each register holder	Ethics Review board and the National Institute for Health and Welfare	Approval from the National Bioethics Committee, Data Protection Authority and from registry holders
Time from application to data delivery	6–12 months	<6 months	6–12 months	12 months	<6 months
Information
Hospitalisations, in-patient care	The Swedish Patient Register 1987	The National Patient Registry 1977	The Norwegian Patient Register 2008	Hospital Finnish Discharge Register 1998	The Icelandic National Patient Registry 1999
Outpatient visits in specialised care	The Swedish Patient Register 2001	The National Patient Registry 1995	The Norwegian Patient Register 2008	Hospital discharge register 1998	No
Primary care	Yes, for three regions (50% of country)	No	No	No	No
Vital status, residency, civil status	The Population Register: 1962	The Civil Registration System 1968	The National Registry: 1946	Population register (date of death) 1969	The Population Register 1914
Cause of death	The Death Register 1952	The Causes of Death Registry 1943	The Cause of Death Registry 1951	No	The Causes of Death Registry 1971
Cancer	The Cancer Registry 1958	The Cancer Registry 1942	The Cancer Registry 1951	The Cancer Registry 1952	The Cancer Registry 1954
Prescribed drugs	The Prescribed Drug Register 2005	The Danish National Database of Reimbursed Prescriptions 2004	The Prescription Database 2004	Co-payment register 2007	The Medicinal Dispense Registry 2002
Education and occupation	The Education Register 1960	Dutch Rheumatoid Arthritis Monitoring Registry 1991	The National Education Database 1970	No	No
Sick leave, disability pension	The Social Insurance Agency Register (MIDAS) 1992 and LISA 1990	IDA registry 1980	The Labour and Welfare Administration 2008	The registers for sick leaves, pensions and rehabilitation 2000	The Social Insurance Administration 1997

LISA, Longitudinal Database for health insurance and labor market studies; MiDAS, Swedish Social Insurance Agency’s database Micro Data for Analysis of Social Insurance.