man-roxygen/args-prior_aux.R

In stan-dev/rstanarm: Bayesian Applied Regression Modeling via Stan

#' @param prior_aux The prior distribution for the "auxiliary" parameter (if
#'   applicable). The "auxiliary" parameter refers to a different parameter 
#'   depending on the \code{family}. For Gaussian models \code{prior_aux} 
#'   controls \code{"sigma"}, the error 
#'   standard deviation. For negative binomial models \code{prior_aux} controls 
#'   \code{"reciprocal_dispersion"}, which is similar to the 
#'   \code{"size"} parameter of \code{\link[stats:NegBinomial]{rnbinom}}:
#'   smaller values of \code{"reciprocal_dispersion"} correspond to 
#'   greater dispersion. For gamma models \code{prior_aux} sets the prior on 
#'   to the \code{"shape"} parameter (see e.g., 
#'   \code{\link[stats:GammaDist]{rgamma}}), and for inverse-Gaussian models it is the 
#'   so-called \code{"lambda"} parameter (which is essentially the reciprocal of
#'   a scale parameter). Binomial and Poisson models do not have auxiliary 
#'   parameters.
#'   
#'   The default prior is described in the vignette 
#'   \href{https://mc-stan.org/rstanarm/articles/priors.html}{\emph{Prior
#'   Distributions for rstanarm Models}}.
#'   If not using the default, \code{prior_aux} can be a call to
#'   \code{exponential} to use an exponential distribution, or \code{normal},
#'   \code{student_t} or \code{cauchy}, which results in a half-normal, half-t,
#'   or half-Cauchy prior. See \code{\link{priors}} for details on these
#'   functions. To omit a prior ---i.e., to use a flat (improper) uniform
#'   prior--- set \code{prior_aux} to \code{NULL}.