Hi, i am investigating individuals being exposed to environmental toxins in early childhood and the risk of development of ADHD. It is a population based cohort study and I did a survival analysis using Poisson regression in proc genmod. Something like this: proc genmod data=temp order=internal; class toxin yeargrp SES; model case=toxin yeargrp SES / dist=poisson link=log offset=lnpyrs type3 covb lrci; run; (lnpyrs are person years) However, I have been made aware that the data have a multi-level structure (subjects within different regions, below the variable f_region), and the analyses should take account of this.  I found that piecewise exponential survival models partition the duration of follow-up into mutually exclusive intervals and fit a model that assumes that the hazard function is constant within each interval. This is equivalent to a Poisson regression model, so I think I should be able to use Proc glimmix and i ran this syntax. Proc glimmix data=temp method=quad; class toxin yeargrp SES f_region; model case=toxin yeargrp SES f_region/ dist=poisson link=log offset=lnpyrs covb cl solution; random intercept / subject=f_region; run; But I am really not sure if this is right?, does the subject=f_region mean that that I actually take the region into account?  I hope to hear from some of you 🙂 Best regards, Malene ... View more