National databases and rheumatology research I: longitudinal databases in Scandinavia

Nationwide population-based longitudinal databases provide excellent resources for medical research. Each Scandinavian country-Sweden, Denmark, Finland, Norway, and Iceland-has its national database, including the Population Registry, the Cancer Registry, the Cause of Death Registry, the Hospital Discharge Registry and others. On a national level, each person has a unique identification code that is used in all registers and allows linking of the data between various registers. Extensive population studies have been conducted in these countries over the last 30 years to supplement registry data. The population of Scandinavia (24,280,000 residents) represents 0.4% of the total world population and 6.4% of the European population; it is almost entirely white, which may limit the generalizability of the observations. Nevertheless, nationwide, population-based databases are only available in Scandinavia. This article describes features of the national databases and provides some examples of rheumatology research that use these databases.