\name{MissingCode}
\alias{MissingCode}
\alias{toString.MissingCode}
\alias{print.MissingCode}
\alias{defaultMissingCodes}
\title{A rule for handling missing outcome variables.}
\description{
  This is a class representing the missing data handling options in an
  \code{amd} object (Assessment Model Description).

  The data set \code{defaultMissingCode} is a list of standard
  \code{MissingCode} objects. 
}
\usage{
MissingCode(type, handler, xmlCode = character(0), checksum = character(0), newval = NULL)
print.MissingCode(x, ...)                               
toString.MissingCode(x, ...)
defaultMissingCodes
}
%- maybe also 'usage' for other objects documented here.
\arguments{
  \item{type}{String giving the type of missing data.  Typically, this is
    one of the values \dQuote{\code{NA}}, \dQuote{\code{Omit}},
    \dQuote{\code{Not Reached}}, or \dQuote{\code{Invalid}}}.
  \item{handler}{String naming the handling strategy to use with this
    type of missing value.  This should be one of the values
    \dQuote{\code{Ingore}}, \dQuote{\code{Low}}, \dQuote{\code{High}},
    \dQuote{\code{Recode}}, or \dQuote{\code{Error}}.}
  \item{xmlCode}{String used to mark this value in a \code{cpd.xml} file.}
  \item{checksum}{Character used to mark this value in a checksum
    attribute of a \code{cpd.xml} file.}
  \item{newval}{If the handler is \dQuote{\code{Recode}}, the new value.}
  \item{x}{Dummy argument to \code{print} or \code{toString}.}
  \item{\dots}{Additional arguments to \code{print} or \code{toString}.}
}
\details{
  StatShop allows several different types of missing data (ie, Not
  Applicable, Omitted, Not Reached, Illegal Value) and offers several
  strategies for handling them (ie, Ignore, Recode, recode to Lowest
  (Highest) possible value.)  The \code{MissingCode} object associates a
  type of missing value with a handling strategy.
}
\value{
  An object of class \code{MissingCode} whose fields are the same as the
  entities given above. 
}
\references{
  \url{http://research.ets.org/~ralmond/StatShop/dataFormats.html}
}
\author{Russell Almond }
\seealso{\code{\link{amd}}, \code{\link{parseMissingCode}},
	 \code{\link{recodeMissingHandlers}}, \code{\link{xmlMissingCode}}}
\examples{
## Ignore (do not score) NAs
MissingCode(type="NA",handler="Ignore", xmlCode="NA",checksum="0")

## Treat Omits as a wrong answer (lowest possible score).
MissingCode(type="Omit",handler="Low", xmlCode="Omit",checksum="*")

## Ignore (do not score) Not Reached observables.
MissingCode(type="Not Reached",handler="Ignore",
            xmlCode="Not Reached",checksum="@")

## Generate an exception for invalid values.
MissingCode(type="Ivalid",handler="Error")

}
\keyword{classes}