# get_prior

From brms v0.7.0
by PaulChristian Buerkner

##### 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 = NULL, family = gaussian(), autocor = NULL,
partial = NULL, threshold = c("flexible", "equidistant"),
internal = FALSE)
```

##### Arguments

- formula
- An object of class "formula" (or one that can be coerced to that class): a symbolic description of the model to be fitted. The details of model specification are given under 'Details'.
- data
- An optional data frame, list or environment (or object coercible by
`as.data.frame`

to a data frame) containing the variables in the model. If not found in data, the variables are taken from`environment(formula)`

, typically t - family
- A description of the error 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.
Currently, the following families are supported:
`gaussian`

- autocor
- An optional
`cor_brms`

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

- partial
- A one sided formula of the form
`~expression`

allowing to specify predictors with category specific effects in non-cumulative ordinal models (i.e. in families`cratio`

,`sratio`

, or`acat`

). - threshold
- 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 thresh - 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 paramter (or parameter class) on which priors can be specified. The prior column is empty except for internal default priors.

##### See Also

##### Examples

```
## 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 fixed effects a once
prior$prior[1] <- "normal(0,10)"
## define a specific prior on the fixed effect of Trt_c
prior$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 0.7.0, License: GPL (>= 3)*

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