I recently encountered an interesting paper by Koster & McElreath (2017) in which they propose a multinomial regression model with random effects that are correlated over each category equation, as shown in the paragraph " The multilevel multinomial behavior model". I am quite new to working with brms but as far as I understand the `family = categorical()`

-argument it by default assumes independence between the random effects in each category. Is there a way around this assumption to fit a model similar to that proposed by Koster & McElreath?

Thanks for your help!