# Specifying priors in mediation model
**URL:** https://discourse.mc-stan.org/t/specifying-priors-in-mediation-model/33514
**Category:** Modeling
**Tags:** brms
**Created:** [December 6, 2023, 6:42pm UTC](https://discourse.mc-stan.org/t/specifying-priors-in-mediation-model/33514 "2023-12-06T18:42:48Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@zbliss623](https://discourse.mc-stan.org/u/zbliss623)
#### Post date: [December 6, 2023, 6:42pm UTC](https://discourse.mc-stan.org/t/specifying-priors-in-mediation-model/33514/1 "2023-12-06T18:42:48Z")
Hi,
I am wondering if anyone knows how I can specify priors by model/formula in something like this brms mediation model:
y\_model ← bf(log\_a\_markdown ~ 1 + lead\_time\_std + us\_penetration + china\_penetration + indonesia\_penetration + canada\_penetration)
m\_model ← bf(lead\_time\_std ~ 1 + us\_penetration + china\_penetration + indonesia\_penetration + canada\_penetration)
a\_md\_mod ← brm(data = df\_home,
family = gaussian,
y\_model + m\_model + set\_rescor(F),
seed = 1555211, iter = 5000, warmup = 500, cores = 4, chains = 4) # we do not want residual correlation
---
### Author:  [@Mauricio\_Garnier-Villarre](https://discourse.mc-stan.org/u/Mauricio_Garnier-Villarre)
#### Post date: [December 11, 2023, 10:40am UTC](https://discourse.mc-stan.org/t/specifying-priors-in-mediation-model/33514/2 "2023-12-11T10:40:43Z")
Hi
you can use the get\_prior function to see what brms is asking from each parameter
```no-highlight
prior <- get_prior(y_model + m_model + set_rescor(F),
data = df_home,
family = gaussian)
```
From there you can modify the prior object to change them for each part of model