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#' @title Rank Responses based on the Wald Test
#'
#' @description Rank responses of a single response question
#' or a multiple response question by the wald test procedure.
#'
#' @usage rank.wald(data, alpha = 0.05, ranktype = 1)
#'
#' @param data A m by n matrix \eqn{d_{ij}}, where \eqn{d_{ij}} = 0 or 1.
#' If the ith respondent selects the jth
#' response, then \eqn{d_{ij}} = 1, otherwise \eqn{d_{ij}} = 0.
#'
#' @param alpha The significance level is used to control the type I error rate.
#' The default is 0.05.
#'
#' @param ranktype A numerical value specifies which type of ranking
#' method is used. The default is 1 (see 'Details').
#'
#' @export rank.wald
#'
#' @details
#' Suppose that the question has k responses.
#' Let \eqn{\pi_{j}} denote the probability that the jth response is selected.
#' Using the survey data, \eqn{\pi_{j}} can be estimated.
#'
#' If \code{ranktype} is 1, the ranking rule is the following steps.
#' Let \eqn{\pi_{(j)}} denote the order statistic.
#' If the hypothesis \eqn{\pi_{(k)}} = \eqn{\pi_{(k-1)}} is rejected,
#' we rank the response corresponding to \eqn{\pi_{(k)}} first.
#' If it is not rejected, we compare \eqn{\pi_{(k)}} with \eqn{\pi_{(j)}}
#' , \eqn{j \le k-2} sequentially.
#'
#' If \code{ranktype} is 2, the rank of the ith response can be defined as
#' \deqn{
#' R_{i} = k - \sum_{j=1, j\ne i}^{k} I(\pi_{i} > \pi_{j})
#' }
#'
#' @return rank.wald returns a table contains the estimated probabilities of the responses being selected in the first line and
#' the ranks of the responses in the second line.
#'
#' @author Hsiuying Wang \email{wang@stat.nycu.edu.tw}
#' , Wan-Ting Huang \email{wthuang.sc09@nycu.edu.tw}
#' , Yu-Chun Lin \email{restart79610@hotmail.com}
#'
#' @references Wang, H. (2008). Ranking Responses in Multiple-Choice Questions.
#' Journal of Applied Statistics, 35, 465-474.
#'
#' Wang, H. and Huang, W. H. (2014). Bayesian Ranking Responses in Multiple Response Questions.
#' Journal of the Royal Statistical Society: Series A (Statistics in Society), 177, 191-208.
#'
#' @seealso \code{\link{rankL2R}}, \code{\link{rankLN}}, \code{\link{rank.gs}}
#'
#' @import stats
#' @importFrom stats qnorm
#'
#' @examples
#' set.seed(12345)
#' # This is an example to rank k responses in a multiple response question
#' # when the number of respondents is 1000.
#' # In this example, we do not use a real data, but generate data in the first six lines.
#' k <- 5
#' data <- matrix(NA, nrow = 1000, ncol = k)
#' for(i in 1:k){
#' p <- runif(1)
#' data[, i] <- sample(c(0, 1), 1000, p = c(p, 1-p), replace = TRUE)
#' }
#' ## or upload the true data
#' rank.wald(data)
#'
rank.wald <- function(data, alpha = 0.05, ranktype = 1)
{
data <- as.matrix(data)
data <- data[!apply(apply(data, 1, is.na), 2, any), ]
n <- dim(data)[1]
k <- dim(data)[2]
z <- qnorm(1 - alpha / 2)
rankiter <- 1L
ordervec <- rank(apply(data, 2, sum), ties.method= "first")
data[, ordervec] <- data[, c(1:k)]
if(ranktype == 1){
y <- c(rep(0, k-1), 1)
i <- k
for(j in (k-1):1){
pi_i <- sum(data[,i]) / n
pi_j <- sum(data[,j]) / n
if((pi_i - pi_j) < 1e-10){
x <- 0
} else {
pi_ij = sum(data[(data[, i] == 1) & (data[, (i-1)] == 1), 1]) / n
x <- (pi_i-pi_j) / sqrt(((pi_i-pi_ij) * (1-pi_i+2*pi_j-pi_ij) + (pi_j-pi_ij) * (1-pi_j+pi_ij)) / n)
}
if(x > z)
{
rankiter <- rankiter + 1L
y[j] <- rankiter
i <- j
} else {
y[j] <- rankiter
}
}
}
if(ranktype == 2){
sumI <- matrix(0, ncol = k, nrow = k)
for(i in 1:k){
for(j in 1:k){
pi_i <- sum(data[, i]) / n
pi_j <- sum(data[, j]) / n
if((pi_i - pi_j) < 1e-10){
x = 0
} else {
pi_ij <- sum(data[(data[, i] == 1) & (data[, (i-1)] == 1), 1]) / n
x <- (pi_i-pi_j) / sqrt(((pi_i-pi_ij) * (1-pi_i+2*pi_j-pi_ij) + (pi_j-pi_ij) * (1-pi_j+pi_ij)) / n)
}
if(x > z)
{
sumI[i, j] <- 1
}
}
}
y <- k - apply(sumI, 1 , sum)
}
data[, c(1:k)] <- data[, ordervec]
y[c(1:k)] <- y[ordervec]
rank <- rank(y, ties.method = "min")
probability <- apply(data, 2, mean)
result <- rbind(probability, rank)
result <- as.table(result)
return(result)
}
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