Hi, I’m learning to use brms but I have a doubt with interactions, this is a basic question, sorry.

I have fit the following model:

fit <- brm_multiple(survival| cens(1-Die) ~ treat+treat*histology, data = imp,family = lognormal(), iter=2000)

Both “treat” and “histology” are binary variables. Subsetting did not work in the imputed dataset (ie. subset = histology==1)

I want to evaluate the posterior probability that “treat” increases survival by 30% in both histology==1 and histology==0. I need something similar to the constrast function in the rms package.

I would also like to know the posterior probability of the interaction.

Thanks.