% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/cvr.R
\name{cvr}
\alias{cvr}
\title{Lawshe's Content Validity Ratio (CVR)}
\usage{
cvr(ratings, essential = 1, na.rm = FALSE)
}
\arguments{
\item{ratings}{A numeric matrix or data frame of expert ratings (rows =
experts, columns = items). A numeric vector is also accepted, treated
as a single item.}

\item{essential}{Numeric vector. Rating value(s) that indicate an expert
classified the item as "essential". Defaults to \code{1}, matching Lawshe's
(1975) original 3-point scale where 1 = essential, 2 = useful but not
essential, 3 = not necessary. Pass a vector if multiple values count
as essential.}

\item{na.rm}{Logical. If \code{TRUE}, missing ratings are excluded when
counting experts. Defaults to \code{FALSE}.}
}
\value{
A named numeric vector of CVR values per item, ranging from -1
to +1. If \code{ratings} is a vector, returns a single numeric value.
}
\description{
Computes Lawshe's (1975) Content Validity Ratio for one or more items
rated by an expert panel. Each expert classifies an item as "essential",
"useful but not essential", or "not necessary"; CVR captures the
proportion of experts endorsing "essential" relative to chance.
}
\details{
The formula is:

\deqn{CVR = (n_e - N/2) / (N/2)}

where \eqn{n_e} is the number of experts rating the item as essential
and N is the total number of experts.

Use \code{\link[=cvr_critical]{cvr_critical()}} to obtain the minimum CVR considered statistically
significant for a given panel size, following the corrected critical
values of Wilson, Pan, and Schumsky (2012).
}
\examples{
# 10 experts rating 3 items on Lawshe's 3-point scale
# (1 = essential, 2 = useful, 3 = not necessary)
ratings <- matrix(
  c(1, 1, 1, 1, 1, 1, 1, 1, 2, 2,    # 8 of 10 essential
    1, 1, 1, 2, 2, 2, 2, 3, 3, 3,    # 3 of 10 essential
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1),   # 10 of 10 essential
  nrow = 10,
  dimnames = list(NULL, paste0("item", 1:3))
)
cvr(ratings)

# Compare to the critical value for N = 10
cvr_critical(10)

}
\references{
Lawshe, C. H. (1975). A quantitative approach to content validity.
\emph{Personnel Psychology}, 28(4), 563-575.
\doi{10.1111/j.1744-6570.1975.tb01393.x}

Wilson, F. R., Pan, W., & Schumsky, D. A. (2012). Recalculation of the
critical values for Lawshe's content validity ratio. \emph{Measurement and
Evaluation in Counseling and Development}, 45(3), 197-210.
\doi{10.1177/0748175612440286}
}
\seealso{
\code{\link[=cvr_critical]{cvr_critical()}}
}
