Parameters | Clinical | Distribution | For AE Time to Event:

For AE Time to Event:
Use this option to choose the distribution the event counts are assumed to follow.
Negative binomial fits an extra parameter k that can account for over-dispersion.
Note : This option is available only when the Response Type is an incidence density.
To Specify the Distribution:
Make sure that either Incidence density based on first event only or Incidence density based on all events is specified as the Response Type .
Note : If s you see errors regarding NEWRAP convergence in the SAS log after you run an ANOVA analytical process with Negative Binomial selected, you should consider either switching to a Poisson distribution or increasing the value specified in the Gradient Convergence Criterion . This will effectively reduce the restrictive criterion and help you avoid this convergence error.