Age-period-cohort analysis of stroke incidence in Dijon from 1985 to 2005.

BACKGROUND AND PURPOSE Variations in stroke incidence could be explained by changes in vascular and environmental factors that affect the risk of stroke and changes in risk factors that are present in early life. The aim of this study was to identify and measure the effects of 3 interrelated factors, age, calendar period of stroke onset, and birth year cohort, on the incidence rates of stroke from 1985 through 2005. METHODS Age-period-cohort models were used to analyze stroke incidence in Dijon from 1985 to 2005 from a population-based registry that collects data on all stroke patients whatever the type of management, in the public hospital, private hospitals, or at home, in the population of Dijon (150,000 inhabitants). RESULTS For ischemic stroke, the incidence rose with time in men depending not only on age, but also on the period and cohort effects (P = 0.017). For women, the incidence only depended on age (P < 0.001; incidence rate ratio, 1.085; 95% CI, 1.081 to 1.089). For hemorrhagic stroke, the rise in the incidence with time depended only on age in men, whereas in women, it depended on age, period, and cohort effects (P = 0.019). CONCLUSIONS Age, birth cohort, and calendar period contain relevant information to define and explain trends in stroke incidence rates over a long period.