Imagine we estimate two sequential negative binomial regressions. In the first one, we use say 3 predictors (x1, x2,x3), and in the second, we use the same 3 plus an additional variable (x4). We are interested in whether x4 change the size of the effect of a specific variable, say x1, in the first model. We observe that incidence rate ratio of X1 is 0.74***, and when x4 included in the second model. it becomes 0.71***. There is a three percent decrease in the IRR, but is this change significant? How can we conclude that x4 reduces the effect of x1 by three percent significantly?



Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy