A Simple Approach to the Estimation of Incidence Rate Difference

摘要

The incidence rate difference (IRD) is a parameter of interest in many medical studies. For example, in vaccinenstudies, it is interpreted as the vaccine-attributable reduction in disease incidence. This is an important parameter,nbecause it shows the public health impact of an intervention. The IRD is difficult to estimate for various reasons,nespecially when there are quantitative covariates or the duration of follow-up is variable. In this paper, the authorsnpropose an approach based on weighted least-squares regression for estimating the IRD. It is very easy tonimplement because it boils down to performing ordinary least-squares regression analysis of transformed vari-nables. Furthermore, if the outcome events are repeatable, the authors propose that data on all events be analyzedninstead of first events only. Four versions of the Huber-White robust standard error are considered for statisticalninference. Simulation studies are used to examine the performance of the proposed method. In a variety ofnscenarios simulated, the method provides an unbiased estimate for the IRD, and the empirical coverage proportionnof the 95% confidence interval is very close to the nominal level. The method is illustrated with data from a vaccinentrial carried out in the Gambia in 2001–2004.