# R_example_confidence_interval.txt
# Population is exponential with mean 2
# Generates a bunch of random sample of size "samplesize" and plots
# a 95% confidence interval for each sample. 
# nci is number of confidence intervals generated

nci=50
samplesize=100

x=c(1:nci)
ybar=c(1:nci)
s=c(1:nci)

for (i in x) {
  y=rexp(samplesize,0.5)
  ybar[i]=mean(y)
  s[i]=sd(y)
}

yl=ybar-1.96*s/sqrt(samplesize)
yu=ybar+1.96*s/sqrt(samplesize)
plot(x,ybar,ylim=c(1,3))
segments(x,yl,x,yu)
abline(h=2.0)