  With advancement of medicine, alternative exposures or interventions are
emerging with respect to a common outcome, and there are needs to formally test
the difference in the associations of multiple exposures. We propose a
duplication method-based multivariate Wald test in the Cox proportional hazard
regression analyses to test the difference in the associations of multiple
exposures with a same outcome. The proposed method applies to linear or
categorical exposures. To illustrate our method, we applied our method to
compare the associations between alignment to two different dietary patterns,
either as continuous or quartile exposures, and incident chronic diseases,
defined as a composite of CVD, cancer, and diabetes, in the Health Professional
Follow-up Study. Relevant sample codes in R that implement the proposed
approach are provided. The proposed duplication-method-based approach offers a
flexible, formal statistical test of multiple exposures for the common outcome
with minimal assumptions.
