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Am J Epidemiol. 2009 Mar 15;169(6):756-60. doi: 10.1093/aje/kwn411. Epub 2009 Feb 11.

Estimation of the relative excess risk due to interaction and associated confidence bounds.

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Department of Epidemiology, School of Public Health, University of North Carolina, Chapel Hill, NC 27599, USA.


The relative excess risk due to interaction (RERI) provides a useful metric of departure from additivity of effects on a relative risk scale. In this paper, the authors show that RERI is identical to the product term in a linear odds ratio or a linear relative risk model. SAS and STATA codes are provided for fitting a linear odds ratio model that directly parameterizes RERI. In addition, this paper presents a method for obtaining likelihood-based 95% confidence bound estimates for RERI. The authors show that likelihood-based confidence intervals may differ substantially from the asymptotic confidence interval estimates advocated by previous authors. The approach presented in this paper should facilitate estimation of RERI and associated likelihood-based confidence bounds, by using standard statistical packages.

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