Aside from using a bound on a fixed effect parameter (i.e ub=0), is there a relatively simple way of constraining a parameter to be negative in brms (maybe something analogous to a lognormal prior for a parameter that is known to be positive)? Or is there a way to put a prior on the negated parameter? It’s only one parameter in my model, so I’m trying to avoid using the somewhat convoluted solution shown in issue 86.

# Constrain parameter to be negative

Not sure about the answer to your original question, but could you make it positive and then multiply the corresponding covariates by -1?

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