# Hitung tCImean confidence interval
    # Confidence Interval calculation, Normal distribution (Z)
    # 
    # Sunu Pradana
    # Samarinda, Indonesia, Agustus 2014
    #		
    # Creative Commons Attribution-ShareAlike 4.0
    # 
    # Usage (contoh penggunaan): 
    # tCImean(95,10,2,5)
    # 
    #
    # CI = confidence interval (arbitrary, usually, 90, 95, or 99)
    # xbar = point estimate of population mean by sample mean
    # es = standard deviation of the sample
    # n = Jumlah sample (sample size)
    #

    tCImean <- function(CI, xbar, es, n){
     
    # CI ; confidence interval
    # xbar ; sample point estimate mean
    # es ; sample standard deviation
    # n ; jumlah sample
          
    alpha = CI/100
     
    two.tail.alpha <- alpha/2
    two.tail.alpha <- 1-alpha
    one.tail.alpha <- two.tail.alpha/2
     
    left.tail.alpha <- one.tail.alpha
    right.tail.alpha <- 1-one.tail.alpha
     
    left.t.value <- qt(left.tail.alpha, n-1)
    right.t.value <- qt(right.tail.alpha, n-1)
     
    left.val <- xbar - ( sqrt(left.t.value^2) * ( es/sqrt(n) ) )
    right.val <- xbar + ( right.t.value * ( es/sqrt(n) ) )
    difr <- ( right.t.value * ( es/sqrt(n) ) )
     
    cat("\n")
    cat( sprintf("CI, xbar, es, n" ),fill = TRUE )
    cat("\n")
     
    cat( sprintf("%-33s %1s % 5.3f  ", "alpha", ":", alpha ),fill = TRUE )
    cat( sprintf("%-33s %1s % 5.3f  ", "two.tail.alpha", ":", two.tail.alpha ),fill = TRUE )
    cat( sprintf("%-33s %1s % 5.3f  ", "one.tail.alpha", ":", one.tail.alpha ),fill = TRUE )
    cat("\n")
    cat( sprintf("%-33s %1s % 5.6g  ", "left.t.value", ":", left.t.value          ),fill = TRUE )
    cat( sprintf("%-33s %1s % 5.6g  ", "left.t.value", ":", round(left.t.value,2) ),fill = TRUE )
    cat("\n")
    cat( sprintf("%-33s %1s % 5.6g  ", "right.t.value", ":", right.t.value         ),fill = TRUE )
    cat( sprintf("%-33s %1s % 5.6g  ", "right.t.value", ":", round(right.t.value,2)),fill = TRUE )
    cat("\n")
    cat( sprintf("%-33s %1s % 4.6g  ", "differ val", ":", round(difr,1)),fill = TRUE )
    cat("\n")
    cat( sprintf("%-33s %1s % 5.6g %12s %-5.4g %-2s ", "left.val",  ":", left.val,  "   [rounded: ", round(left.val,1), "]"  ),fill = TRUE )
    cat( sprintf("%-33s %1s % 5.6g  ", "Point estimate of population mean", ":", xbar ),fill = TRUE )
    cat( sprintf("%-33s %1s % 5.6g %12s %-5.4g %-2s ", "right.val", ":", right.val, "   [rounded: ", round(right.val,1),"]" ),fill = TRUE )
    cat("\n")
    }