Time to first event is modeled using PROC LIFETEST in SAS/STAT. A test of differences of time to first event across treatment groups is conducted using both Log -Rank and Wilcoxon statistics. A volcano plot of each of these is produced using the maximum difference between Kaplan-Meier curves on the x -axis and -log 10 ( p -value) of the corresponding test on the y -axis.Incidence densities compare the proportion of occurrences of events across treatment groups. Data for incidence density, based on the first event only, are aggregated to the treatment level whereas data for incidence density based on all events are aggregated to the subject level. Both are modeled using PROC GENMOD with a Poisson or negative binomial distribution, log link, and log person-year offset.