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 different value than b_Intercept.

Should I set a prior for this? I am working with a custom family where the default priors usually don’t make much sense.

A minimal example on what the Intercept and b_Intercept can look like in a very simple model:

```
data = data.frame(x = c(1,2,2,1,4,5,6,5), y = c(1,1,1,1,2,2,2,2))
test_fit1 = brm(data = data,
formula = x ~ y,
seed = 1,
save_pars = save_pars(all=TRUE))
summary(test_fit1)
test_fit1$fit
mcmc_plot(test_fit1, pars = c('Intercept', 'y', 'sigma'))
```

the output of test_fit1$fit

```
mean se_mean sd 2.5% 25% 50% 75% 97.5% n_eff Rhat
b_Intercept -2.00 0.02 1.03 -4.16 -2.59 -2.00 -1.41 0.08 2536 1
b_y 3.50 0.01 0.66 2.16 3.12 3.49 3.86 4.84 2574 1
sigma 0.90 0.01 0.35 0.48 0.66 0.81 1.04 1.79 1406 1
Intercept 3.24 0.01 0.34 2.53 3.05 3.25 3.44 3.88 2154 1
lp__ -13.30 0.05 1.52 -17.26 -14.02 -12.90 -12.16 -11.56 1083 1
```

P.S. I am pretty new to this so I apologize if this should be obvious. Any hints are appreciated