\name{ckappa}
\alias{ckappa}
\title{Cohen's Kappa for 2 raters}
\description{Computes Cohen's Kappa for agreement in the case of 2 raters. The diagnosis (the object of the rating) may have k possible values.}
\usage{ckappa(r)}
\arguments{
  \item{r}{n*2 matrix or dataframe, n subjects and 2 raters}}
\details{The function deals with the case where the two raters have not exactly the same scope of rating (some software associate an error with this situation).
Missing value are omitted.}
\value{A list with :
  \item{$table}{the 2*k table of raw data (first rater in rows, second rater in columns)}
  \item{$kappa}{Cohen's Kappa}}
\references{Cohen, J. (1960), A coefficient of agreement for nominal scales, Educational and Psychological measurements, 20, 37-46.}
\author{Bruno Falissard}
\examples{data(expsy)
ckappa(expsy[,c(12,14)])          # Cohen's kappa for binary diagnosis

#to obtain a 95%confidence interval:
#library(boot)
#ckappa.boot <- function(data,x) {ckappa(data[x,])[[2]]}
#res <- boot(expsy[,c(12,14)],ckappa.boot,1000)
#quantile(res$t,c(0.025,0.975))    # two-sided bootstrapped confidence interval of kappa
#boot.ci(res,type="bca")           # adjusted bootstrap percentile (BCa) confidence interval (better)
#ckappa(expsy[,c(11,13)])          # Cohen's kappa for non binary diagnosis
}
\keyword{univar}