On Fri, Nov 30, 2012 at 9:47 AM, jaybell <stephe...@yahoo.com.tw> wrote: > a=c(0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9) > b=c(0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1) > cor(a,b)= -1 > > a'=qbinom(a, 1, 0.5) > b'=qbinom(b, 1, 0.5) > why cor(a',b') becomes -0.5 ?
On my computer the correlation is -0.8. It is not 1 because you did a non-linear transformation of a and b. Plot a vs. b, then plot a' vs b' and you will see why the correlation is not -1: a vs b is a straight line, a' vs b' is not a straight line. Peter ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
