I am trying to use the posterior_linpred function in brms to get predictions across one grouping variable, which has random intercepts and random slopes, while marginalizing over (excluding) the random effects of other grouping variables. I understand that I need to use the re_formula argument to accomplish this, but I have a question about the proper syntax.
In a model with both random intercepts and random slopes, does
re_formula = ~ (1|group) include all random effects, or just the intercept? If I try
re_formula = ~ (1 + slope|group) I get an error for repeating a group in the re formula.