In a Poisson model, do we need to check for multicollinearity between the offset variable and other covariates? For example, if I offset by population size, would it be problematic to include covariates that are correlated with population?

  • $\begingroup$ It is not problematic. In most software packages, the offset is specified inside of a function. In R, for example, glm(y ~ x + offset(log(population))...), where population size is the offset/exposure variable. $\endgroup$ – Thomas Bilach May 25 at 4:48

No. In a count model, the offset/exposure variable is not a covariate. Rather than being estimated as a coefficient, its value is constrained to equal 1. It allows you to model rates instead of counts. I would review this post for more information.

Incorporating additional predictors that may be correlated with population size should not concern you if you're using population as your offset.

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  • $\begingroup$ Thanks, Thomas! I appreciate your clear response. $\endgroup$ – Sahit Menon May 25 at 23:31

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