# get_prior

##### Overview on Priors for brms Models

Get information on all parameters (and parameter classes) for which priors may be specified including default priors.

##### Usage

```
get_prior(formula, data, family = gaussian(), autocor = NULL,
nonlinear = NULL, threshold = c("flexible", "equidistant"),
internal = FALSE)
```

##### Arguments

- formula
An object of class

`formula`

or`brmsformula`

(or one that can be coerced to that classes): A symbolic description of the model to be fitted. The details of model specification are explained in`brmsformula`

.- data
An object of class

`data.frame`

(or one that can be coerced to that class) containing data of all variables used in the model.- family
A description of the response distribution and link function to be used in the model. This can be a family function, a call to a family function or a character string naming the family. Every family function has a

`link`

argument allowing to specify the link function to be applied on the response variable. If not specified, default links are used. For details of supported families see`brmsfamily`

. By default, a linear`gaussian`

model is applied.- autocor
An optional

`cor_brms`

object describing the correlation structure within the response variable (i.e., the 'autocorrelation'). See the documentation of`cor_brms`

for a description of the available correlation structures. Defaults to`NULL`

, corresponding to no correlations.- nonlinear
(Deprecated) An optional list of formulas, specifying linear models for non-linear parameters. If

`NULL`

(the default)`formula`

is treated as an ordinary formula. If not`NULL`

,`formula`

is treated as a non-linear model and`nonlinear`

should contain a formula for each non-linear parameter, which has the parameter on the left hand side and its linear predictor on the right hand side. Alternatively, it can be a single formula with all non-linear parameters on the left hand side (separated by a`+`

) and a common linear predictor on the right hand side. As of brms 1.4.0, we recommend specifying non-linear parameters directly within`formula`

.- threshold
(Deprecated) A character string indicating the type of thresholds (i.e. intercepts) used in an ordinal model.

`"flexible"`

provides the standard unstructured thresholds and`"equidistant"`

restricts the distance between consecutive thresholds to the same value. As of brms 1.8.0, we recommend specifying threshold directly within the ordinal family functions.- internal
A flag indicating if the names of additional internal parameters should be displayed. Setting priors on these parameters is not recommended

##### Value

A data.frame with columns `prior`

, `class`

, `coef`

, and `group`

and several rows, each providing information on a parameter (or parameter class) on which
priors can be specified. The prior column is empty except for internal default priors.

##### See Also

##### Examples

```
# NOT RUN {
## get all parameters and parameters classes to define priors on
(prior <- get_prior(count ~ log_Age_c + log_Base4_c * Trt_c
+ (1|patient) + (1|visit),
data = epilepsy, family = poisson()))
## define a prior on all population-level effects a once
prior$prior[1] <- "normal(0,10)"
## define a specific prior on the population-level effect of Trt_c
prior$prior[5] <- "student_t(10, 0, 5)"
## verify that the priors indeed found their way into Stan's model code
make_stancode(count ~ log_Age_c + log_Base4_c * Trt_c
+ (1|patient) + (1|visit),
data = epilepsy, family = poisson(),
prior = prior)
# }
```

*Documentation reproduced from package brms, version 1.10.2, License: GPL (>= 3)*