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Methods and results

The basic data source was the Finnish child welfare registry. The data were completed by individual linkage with the Finnish cause of death registry, using the personal identification number of each child. The study covered all children in Finland who were taken into care between 1 January 1991 and 31 December 1997 (n= 13 371). One per cent (133) could not be linked to the cause of death registry owing to errors in the personal identification number. All subjects were born between 1 January 1973 and 31 December 1997 and followed up until 31 December 1999 or, if earlier, their 25th birthday or, if earlier, their death. During the study period 106 individuals (32 females and 74 males) died. Mortality ratios standardised for age were used to compare the mortality of children in the cohort (girls and boys separately) with that of the general population of the same age in Finland.