Expoisson command error: factor-variable and time-series operators not allowed

[Sakshi Rajatbhai Tewari]

I am running an expoisson model on a summarized dataset and faced a issue when i added a covariate with 3 categories.

expoisson NADM i.yearcat, exposure(Persondays) irr

Any one know a workaround? i want IRRs of each category compared to the first..
Thanks

[Rich Goldstein]

use the -xi- prefix; see

h xi

[Sakshi Rajatbhai Tewari]

I think that worked! thank you- this is so useful for similar models that dont allow factor variables.