R/simple.z.test.R

In jverzani/UsingR: Data Sets, Etc. for the Text "Using R for Introductory Statistics", Second Edition

##' find CI from a z test (known sigma)
##'
##' @param x data
##' @param sigma known population standard deviation
##' @param conf.level confidence level
##' @return a confidence interval
##'
##' @export
simple.z.test <-function(x,sigma,conf.level=0.95) {
  n <- length(x);xbar<-mean(x)
  alpha <- 1 - conf.level
  zstar <- qnorm(1-alpha/2)
  SE <- sigma/sqrt(n)

  xbar + c(-zstar*SE,zstar*SE)
}