I noticed that when I set save_pars = save_pars(all=TRUE) there is a parameter called b_Intercept and one called Intercept in my model. Intercept does not show up in the summary, but in the $fit. When not all parameters are saved, there is only b_Intercept. What does Intercept mean? It has a diff…

Hi Britta, If you look at the underlying Stan code for the model using: make_stancode(data = data, formula = x ~ y, seed = 1, save_pars = save_pars(all=TRUE)) You’ll see the respective definitions: parameters { vector[Kc] b; // population-level effects real Intercept; // tempor…

Thank you for the suggestion, unfortunately reading it did not help me. If I am not mistaken, the model I specify above is x ~ N(b_Intercept + b_y * y, sigma) So what do I need the additional parameter ‘Intercept’ for?

To start with data should be data = data.frame(x = c(1,2,2,1,4,5,6,5), y = c(1,1,1,1,2,2,2,2))

Your are right, of course. I edited my original post.

Thanks for cleaning up the code. That will help other folks who have the same question. Let me tag in some brms folks. I looked this up once but have since forgotten. @paul.buerkner

To OPs question about setting a prior for Intercept, I’ve read a couple of posts that suggest that the prior we set with class “Intercept” should be for the mean-centered scaled parameter, i.e. “Intercept” not “b_Intercept”. Is that also your understanding?

To understand the distinction between what brms calls “Intercept” and “b_Intercept,” you want to spend some time reading through the Parameterization of the population-level intercept and set_prior sections of the brms reference manual . This generally isn’t a big deal if you use default priors (whic…

What is the difference between Intercept and b_Intercept?

Modeling

Ara_Winter January 25, 2021, 7:04pm 2

Is this what you are looking for Difference between b & Intercept classes in brms ?

Topic		Replies	Views
Understanding intercept prior in brms brms	11	2624	May 12, 2025
b_Intercept and Intercept: how are they related? brms	5	1625	February 3, 2020
Difference between b & Intercept classes in brms Modeling rstan	3	2198	July 27, 2020
Setting an intercept prior on a regression in brms General	2	110	November 19, 2025
Why does model run with cmdstanr as_draws() have both b_Intercept and Intercept Modeling brms	3	489	February 16, 2023

What is the difference between Intercept and b_Intercept?

Related topics