I am conducting a post-marketing safety surveillance study in which I have defined both my study cohort and the outcomes of interest. I have calculated the incidence rates (IRs) for these outcomes; however, I am now considering how to interpret the statistical significance of these IRs. Specifically, I am unsure whether I should compare my findings against a background incidence rate or instead examine incidence rates before and after exposure to the medicine. Could you please advise on the appropriate approach, or suggest alternative methods to assess the significance of the observed incidence rates?