select_parameters.Rd

% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/select_parameters.R
\name{select_parameters}
\alias{select_parameters}
\alias{select_parameters.lm}
\alias{select_parameters.merMod}
\title{Automated selection of model parameters}
\usage{
select_parameters(model, ...)

\method{select_parameters}{lm}(model, direction = "both", steps = 1000, k = 2, ...)

\method{select_parameters}{merMod}(model, direction = "backward", steps = 1000, ...)
}
\arguments{
\item{model}{A statistical model (of class \code{lm}, \code{glm}, or \code{merMod}).}

\item{...}{Arguments passed to or from other methods.}

\item{direction}{
    the mode of stepwise search, can be one of \code{"both"},
    \code{"backward"}, or \code{"forward"}, with a default of \code{"both"}.
    If the \code{scope} argument is missing the default for
    \code{direction} is \code{"backward"}.  Values can be abbreviated.
  }

\item{steps}{
    the maximum number of steps to be considered.  The default is 1000
    (essentially as many as required).  It is typically used to stop the
    process early.
  }

\item{k}{The multiple of the number of degrees of freedom used for the penalty.
Only \code{k = 2} gives the genuine AIC: \code{k = log(n)} is sometimes referred to as
BIC or SBC.}
}
\value{
The model refitted with optimal number of parameters.
}
\description{
This function performs an automated selection of the 'best' parameters,
updating and returning the "best" model.
}
\section{Classical lm and glm}{

For frequentist GLMs, \code{select_parameters()} performs an AIC-based stepwise
selection.
}

\section{Mixed models}{

For mixed-effects models of class \code{merMod}, stepwise selection is based on
\code{\link[cAIC4:stepcAIC]{cAIC4::stepcAIC()}}. This step function only searches the "best" model
based on the random-effects structure, i.e. \code{select_parameters()} adds or
excludes random-effects until the cAIC can't be improved further.
}

\examples{
\dontshow{if (requireNamespace("lme4")) withAutoprint(\{ # examplesIf}
model <- lm(mpg ~ ., data = mtcars)
select_parameters(model)

model <- lm(mpg ~ cyl * disp * hp * wt, data = mtcars)
select_parameters(model)
\donttest{
# lme4 -------------------------------------------
model <- lme4::lmer(
  Sepal.Width ~ Sepal.Length * Petal.Width * Petal.Length + (1 | Species),
  data = iris
)
select_parameters(model)
}
\dontshow{\}) # examplesIf}
}