Danish registers contain information on many important health and social issues. Because all Danish citizens have a unique personal identification number, linkage at the individual level between these nationwide registers and other data sources is possible and feasible. In this paper we briefly introduce selected Danish registers and the data structure and requirements for getting access to data at Statistics Denmark, which is the main provider of register data. We introduce the Danish Data Archive and briefly present the Act on Processing of Personal Data, which is the legal foundation for analyses of registerbased data in Denmark.

The Danish Multiple Sclerosis Registry contains information about all Danish patients in whom multiple sclerosis has been diagnosed since 1948. The purpose of this study was to analyse trends in survival and causes of death of these patients and to compare them with those of the general population. The study comprised all patients with onset in the period 1949-1996. All case records were validated and classified according to standardized diagnostic criteria. Data on emigration and death were obtained by record linkage to official registers. The end of follow-up was 1 January 2000 for emigration and death, and 1 January 1999 for cause-specific deaths. Standardized mortality ratios and excess death rates were calculated for various causes of death and periods after multiple sclerosis onset, and time trends in survival probability were analysed by Cox regression. The study comprised 9881 patients, of whom 4254 had died before end of follow-up. The median survival time from onset was approximately 10 years shorter for multiple sclerosis patients than for the age-matched general population, and multiple sclerosis was associated with an almost threefold increase in the risk for death. According to death certificates, more than half (56.4%) of the patients had died from multiple sclerosis. They also had excess mortality rates from other diseases, except cancer, and from accidents and suicide. The probability for survival improved significantly during the observation period. Thus, the 10-year excess mortality was almost halved in comparison with that in the middle of the 1900s.

Background and Purpose-As part of the Danish contribution to the World Health Organization (WHO) MONICA (Monitoring Trends and Determinants in Cardiovascular Disease) Project, a register of patients with stroke was established in 1982. The purpose of the present study was to analyze long-term survival and causes of death after a first stroke and to compare them with those of the background population. Methods-The study population comprised all subjects aged 25 years or older who were resident in a geographically defined region in Copenhagen County. All stroke events in the study population during 1982-1991 were ascertained and validated according to standardized criteria outlined for the WHO MONICA Project. After completion of the stroke registry at the end of 1991, all patients were followed up by record linkage to official registries. Standardized mortality ratios were calculated for various causes of death and periods after the stroke. Results-The estimated cumulative risks for death at 28 days, 1 year, and 5 years after onset were 28%, 41%, and 60%, respectively. Compared with the general population, nonfatal stroke was associated with an almost 5-fold increase in risk for death between 4 weeks and 1 year after a first stroke and a 2-fold increase in the risk for death subsequent to 1 year. The excess mortality rate in stroke patients was due mainly to cardiovascular diseases but also to cancer, other diseases, accidents, and suicide. The probability for long-term survival improved significantly during the observation period for patients with ischemic or ill-defined stroke. Conclusions-Stroke is a medical emergency associated with a very high risk for death in the acute and subacute phases and with a continuous excess risk of death. Better prevention and management of strokes may improve the long-term survival rate.

The calculated mean values for the EQ-5D index score may be used as reference values for comparative purposes in future Danish population health and evaluative studies.

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