DOI: 10.2337/dc06-1568 © 2007 by the American Diabetes Association
Spatiotemporal Trends and Age-Period-Cohort Modeling of the Incidence of Type 1 Diabetes Among Children Aged <15 Years in Norway 19731982 and 19892003
1 EpiGen, Akershus University Hospital, Lørenskog, Norway Address correspondence and reprint requests to Geir Aamodt, Division of Epidemiology, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, N-0403 Oslo, Norway. E-mail: geir.aamodt{at}fhi.no OBJECTIVEWe have investigated age-period-cohort effects and spatial and temporal trends for the incidence of type 1 diabetes among 0- to 14-year-old children in Norway. RESEARCH DESIGN AND METHODSWe included children with the diagnosis of type 1 diabetes in Norway during 19731982 and 19892003. We studied age, calendar period, and birth cohort effects using Poisson regression, including Holford's method of parameterization, to model the dependencies between age, period, and cohort effects. To study spatiotemporal clustering of cases, we used spatial scan statistics. RESULTSThe overall incidence rate for the study population <15 years of age was 22.7 cases per 100,000 (95% CI 22.123.4), showing an average annual increase of 1.2% (95% CI 0.71.5%) during the study period. One specific area with 30% increased incidence rates was identified in the southern part of Norway during 19761980 (P = 0.001). Also, children born during 19641966 in a specific region in the southern part of Norway as well as children born during 19871989 in a region in northern Norway showed 2.0 and 2.6 times, respectively, higher incidence rates compared with the rest of the country (both P = 0.001). CONCLUSIONSThe incidence of type 1 diabetes among children increased during the study period. Birth cohort effects were identified using the spatiotemporal scan statistic but not using age, period, and birth cohort modeling. Such effects, within the relatively homogenous Norwegian population, suggest the influence of nongenetic etiological factors.
Abbreviations: APC, age-period-cohort
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