= R code for bootstrapped confidence intervals for means and medians from a skewed sample =

The above codes generates the results from the [[http://imaging.mrc-cbu.cam.ac.uk/statswiki/StatsCourse2007|exploratory data analysis grad talk]] and shows the undue influence of outliers in computing means from skewed data.

{{{
y <- c(0,0,0,4,4,5,5,5,6,6,6,6,6,6,6)

nsamp <- 1000

b <- rep(0,nsamp)
c <- rep(0,nsamp)

for (j in 1:nsamp) {
x <- 1:15

yb <- sample(x, size=15, replace=T)

y2 <- y[yb]

b[j] <- median(y2)
c[j] <- mean(y2)

}

% Estimate of the mean of the median

md <- median(b)
mn <- median(c)

% 95% CI
% make sure nsamp is a multiple of 20

bs <- sort(b)
ind <- trunc(0.05*nsamp)
bs[ind]
ind <- trunc(0.95*nsamp)
bs[ind]

cs <- sort(c)
ind <- trunc(0.05*nsamp)
cs[ind]
ind <- trunc(0.95*nsamp)
cs[ind]
}}}