The Danish Civil Registration System. A cohort of eight million persons.

The Danish Civil Registration System (CRS) was established in 1968, where all persons alive and living in Denmark were registered. Among many other variables, it includes individual information on personal identification number, gender, date of birth, place of birth, place of residence, citizenship, continuously updated information on vital status, and the identity of parents and spouses. To evaluate the quality and completeness of the information recorded on persons in the CRS, we considered all persons registered on November 4, 2005, i.e. all persons who were alive and resident in Denmark at least one day from April 2, 1968 to November 4, 2005, or in Greenland from May 1, 1972 to November 4, 2005. A total of 8,176,097 persons were registered. On November 4, 2005, 5,427,687 (66.4%) were alive and resident in Denmark, 56,920 (0.7%) were alive and resident in Greenland, 2,141,373 (26.2%) were dead, 21,160 (0.3%) had disappeared, and 528,957 (6.5%) had emigrated. Among persons born in Denmark 1960 or later the CRS contains complete information on maternal identity. Among persons born in Denmark 1970 or later the CRS contains complete information on paternal identity. Among women born in Denmark April 1935 or later the CRS contains complete information on all their children. Among males born in Denmark April 1945 or later the CRS contains complete information on all their children. The CRS contains complete information on: a) immigrations and emigrations from 1971 onwards, b) permanent residence in a Danish municipality from 1971 onwards, c) permanent residence in a municipality in Greenland from May 1972 onwards, and d) full address in Denmark from 1977 onwards. Data from the CRS is an important research tool in epidemiological research, which enables Danish researchers to carry out representative population-based studies on e.g. the potential clustering of disease and death in families and the potential association between residence and disease and death.