The International journal of risk & safety in medicine
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The present thesis, which is based on a review and 12 published articles, concerns clinical epidemiological methods [176-187]. The Nordic countries have for many years established numerous registries. The establishment in Denmark of the National Population Registry in 1924 and the personal registration number (the CPR number) in 1968 allowed person-identification of remarkable quality, and made it possible to gather information on the same person in several registries. ⋯ This allows for comparison with respect to the completeness and validity of the data. The use of discharge diagnoses from hospital registries involves considerable data quality problems, while data from the health service registries, and from the public health officers' surveillance system for strong analgesics and notifiable diseases are of satisfactory quality. Misclassification of data exists, however, in all data sources; this can only be revealed by comprehensive studies of the validity of the data quality.