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JtTest <- function(formula, data, alpha = 0.05, na.rm = TRUE, verbose = TRUE) {
dp=as.character(formula)
DNAME <- paste(dp[[2L]], "and", dp[[3L]])
METHOD <- "Jonckheere-Terpstra Test"
TEST <- "JT"
if (na.rm){
completeObs <- complete.cases(data)
data <- data[completeObs,]
}
if (any(colnames(data)==dp[[3L]])==FALSE) stop("The name of group variable does not match the variable names in the data. The group variable must be one factor.")
if (any(colnames(data)==dp[[2L]])==FALSE) stop("The name of response variable does not match the variable names in the data.")
y = data[, dp[[2L]]]
group = data[, dp[[3L]]]
if (!is.factor(group)) stop("The group variable must be a factor.")
if (!is.numeric(y)) stop("The response must be a numeric variable.")
n <- length(y)
x.levels <- levels(factor(group))
k=NROW(x.levels)
JT =0;s=1
y.n <- NULL
for (i in x.levels) {
y.n[i] <- length(y[group==i])
}
for (i in x.levels[1:k-1])
{s=s+1
for (j in x.levels[s:k]) {
A <- rank(y[group==i|group==j])
JT=JT+sum(A[(y.n[i]+1):(y.n[i]+y.n[j])])-NROW(y[group==j])*(NROW(y[group==j])+1)/2
}}
a=sum(y.n^2);
b=sum((y.n^2)*(2*y.n+3))
EJT=(n^2-a)/4
VJT=((n^2*(2*n+3))-b)/72
Z=(JT-EJT)/sqrt(VJT)
p.value=1-pnorm(Z, mean = 0, sd = 1, lower.tail = TRUE, log.p = FALSE)
if (verbose) {
cat("---------------------------------------------------------","\n", sep = " ")
cat(" Test :", METHOD, "\n", sep = " ")
cat(" data :", DNAME, "\n\n", sep = " ")
cat(" Statistic =", JT, "\n", sep = " ")
cat(" Mean =", EJT, "\n", sep = " ")
cat(" Variance =", VJT, "\n", sep = " ")
cat(" Z =", Z, "\n", sep = " ")
cat(" Asymp. p-value =", p.value, "\n\n", sep = " ")
cat(if (p.value > alpha) {" Result : Null hypothesis is not rejected."}
else {" Result : Null hypothesis is rejected."}, "\n")
cat("---------------------------------------------------------","\n\n", sep = " ")
}
result <- list()
result$statistic <- JT
result$mean <- EJT
result$variance <- VJT
result$Z <- Z
result$p.value <- p.value
result$alpha <- alpha
result$method <- METHOD
result$data <- data
result$formula <- formula
attr(result, "class") <- "owt"
invisible(result)
}
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