Abstract:
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In safety studies, the incremental incidence rate is a useful concept in evaluating risks related to adverse events of medical interest (EMI). We propose estimates for the incremental (say annual)incidence rates and describe their statistical properties. More importantly, we propose tests for the null hypothesis that the incremental incidence rates remain constant during the study against various alternative hypotheses, such as rates changing over the years or having a specific trend, say monotonic increasing or decreasing. In contrast with the existing methods that test constant hazard rates, the proposed method allows non-constant hazard within each year; therefore, it is especially useful for EMIs that have a seasonal occurrence pattern. This article explores and characterizes properties of these tests under various alternatives via theory and simulations. A numerical example based on a real long-term single cohort safety study is also provided to demonstrate the application and interpretation of the proposed tests. It also illustrates limitations of visually inspecting the rates, as opposed to formally testing them, to assert a causal link between exposure and adverse EMIs.
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