in base R it is possible to specify a two-column matrix as outcome in a binomial glm, where the first column is a fraction and the second indicates the total counts, like so:
glm(cbind(frac, counts) ~ x, data=dat, family=binomial)
I tried that in rstanarm but that doesn’t seem to be supported:
Error: All outcome values must be counts for binomial models.
Does somebody know a workaround or if/how to specify something like that in brms?