#' Generate a data.frame of diagnostic accuracy study.
#'
#' Generate a data.frame of diagnostic accuracy study given true negative, true
#' positive, false negative, false positive.
#'
#'
#' @param tn True negative
#' @param tp True positive
#' @param fn False negative
#' @param fp False positive
#' @return A data.frame for diagnostic accuracy studies.
#' @examples
#'
#' db <- dadb(tn=720, tp=190, fn=10 , fp=80)
#' with(db, table(test,refstd))
#'
#' @export
dadb <- function(tn,tp,fn,fp) {
test <- factor(rep(c("+", "-"), c(tp + fp, tn + fn)),
levels=c("-", "+"))
refstd <- factor(c(rep("present", tp),
rep("absent", fp),
rep("present", fn),
rep("absent", tn)),
levels=c("absent","present"))
rval <- data.frame(refstd, test)
## put in order of reference standard
rval[with(rval, order(refstd, test)), ]
}
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