REGIONAL DIFFERENCES IN THE INCIDENCE OF INSULIN-DEPENDENT DIABETES-MELLITUS AMONG CHILDREN IN FINLAND FROM 1987 TO 1991

The regional pattern of insulin-dependent diabetes mellitus (IDDM) inc idence among children in Finland was analysed applying several methods attempting to describe the geographical variation in occurrence of ID DM. From 1987 to 1991 the number of newly diagnosed cases aged 14 year s or less at diagnosis was 1728. The incidence, the incidence rate rat io and the Bayes relative risk (RR) for IDDM were calculated by munici pality, by functional area (an urban centre with a subordinated surrou nding area) and by area with a population of equal size at risk employ ing the Geographical Information Systems. The association of IDDM inci dence with the degree of urbanization was assessed using the populatio n density as a criterion for the degree of urbanization. The overall m ean of the IDDM incidence was 35 per 100000 persons per year. Between municipalities the incidence varied from 4 to 245 per 100000 persons p er year, whereas a clear regional pattern was seen among the functiona l areas and the incidence varied from 26 to 43 per 100000 persons per year. The RR for IDDM among the municipalities ranged from 0.82 to 1.3 4 and from 0.73 to 1.27 among the functional areas. The incidence dete rmined in four zones with the same size of population was the highest in the middle part of the country. There was a strong inverse correlat ion between population density and the incidence of IDDM and this also applied to the relationship between child population density and inci dence.