Calculating Absolute rate reductions with Count Data

#1
Hello everyone,
I'm analyzing count data in stata using negative binomial regression because of overdispersion. I'm reporting incident rate ratios using the model I've described below. Is there also a way to calculate an absolute rate reduction based on the level of exposure? This study is policy related, so I think reporting the absolute rate reduction would be of additional benefit.


Exposure: 4 level categorial variable
Outcome: Injury count
Covariables: several continuous variables
Offset: log of the population at risk
Clustered at the state level b/c of correlated data.


Thanks for any advice you can offer.