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Simulation study of the bias of the pairwise Cox likelihood method and the original prior event rate ratio (PERR) adjustment method in the presence of an interaction between hidden confounder and treatment. Graphs are based on simulated dataset of n = 100,000 paired event times. An exponential baseline hazard was used with a rate parameter of 1. The main effect of treatment was θ = 1, and the period effect was α = 1. β 1 denotes the size of the interaction effect.
