Age-Period-Cohort Analysis of 1990–2003 Incidence Time Trends of Childhood Diabetes in Italy
The RIDI Study
- Graziella Bruno1,
- Milena Maule2,
- Franco Merletti2,
- Giulia Novelli1,
- Alberto Falorni3,
- Antonio Iannilli4,
- Lorenzo Iughetti5,
- Emma Altobelli6,
- Giuseppe d'Annunzio7,
- Silvano Piffer8,
- Paolo Pozzilli9,
- Dario Iafusco10,
- Marco Songini11,
- Federico Roncarolo12,
- Sonia Toni13,*,
- Flavia Carle14,*,
- Valentino Cherubini4,* and
- the RIDI Study Group†
- 1Department of Internal Medicine, University of Turin, Turin, Italy;
- 2Cancer Epidemiology Unit, CeRMS and CPO Piemonte, University of Turin, Turin, Italy;
- 3Department of Internal Medicine, University of Perugia, Perugia, Italy;
- 4Department of Pediatrics, Polytechnic University of Marche, Ancona, Italy;
- 5Department of Pediatrics, University of Modena, Modena, Italy;
- 6Department of Epidemiology, University of L'Aquila, L'Aquila, Italy;
- 7Department of Pediatrics, University of Genova, Genova, Italy;
- 8Unit of Observational Epidemiology, Trento, Italy;
- 9Università Campus Bio-Medico, University of Rome, Rome, Italy;
- 10Department of Pediatrics, University of Napoli, Napoli, Italy;
- 11S. Michele Hospital, Cagliari, Italy;
- 12Department of Preventive Medicine, University of Pavia, Pavia, Italy;
- 13Department of Pediatrics, University of Florence, Florence, Italy;
- 14Department of Epidemiology, Biostatistics and Medical Information Technology, Polytechnic University of Marche, Ancona, Italy.
- Corresponding author: Graziella Bruno, .
G.B. and M.M. contributed equally to this study.
OBJECTIVE To investigate age-period-cohort effects on the temporal trend of type 1 diabetes in children age 0–14 years in Italian registries.
RESEARCH DESIGN AND METHODS This report is based on 5,180 incident cases in the period 1990–2003 from the Registry for Type 1 Diabetes Mellitus in Italy (RIDI). Multilevel (random intercept) Poisson regression models were used to model the effects of sex, age, calendar time, and birth cohorts on temporal trends, taking into account the registry-level variance component.
RESULTS The incidence rate was 12.26 per 100,000 person-years and significantly higher in boys (13.13 [95% CI 12.66–13.62]) than in girls (11.35 [10.90–11.82]). Large geographical variations in incidence within Italy were evident; incidence was highest in Sardinia, intermediate in Central-Southern Italy, and high in Northern Italy, particularly in the Trento Province, where the incidence rate was 18.67 per 100,000 person-years. An increasing temporal trend was evident (2.94% per year [95% CI 2.22–3.67]). With respect to the calendar period 1990–1992, the incidence rates increased linearly by 15, 27, 35, and 40% in the following time periods (P for trend < 0.001). With respect to the 1987–1993 birth cohort, the incidence rate ratio increased approximately linearly from 0.63 (95% CI 0.54–0.73) in the 1975–1981 cohort to 1.38 (1.06–1.80) in the 1999–2003 cohort. The best model, however, included sex, age, and a linear time trend (drift).
CONCLUSIONS Large geographical variations and an increasing temporal trend in diabetes incidence are evident among type 1 diabetic children in Italy. Age-period-cohort analysis shows that the variation over time has a linear component that cannot be ascribed to either the calendar period or the birth cohort.
*RIDI Study Group coordinators.
†A complete list of the RIDI Study Group is available in the appendix.
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- Received January 31, 2010.
- Accepted June 10, 2010.
- © 2010 by the American Diabetes Association.
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