Dear Peter, I assumed that Carol wanted to compare the shapes of the distributions and to adjust for differences in centre and spread. To put a line through the quartiles or to base a line on the medians and IQRs is more robust than using the means and sds.
Best, John > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Peter Flom > Sent: November-02-09 11:57 AM > To: carol white; Yihui Xie > Cc: r-h...@stat.math.ethz.ch > Subject: Re: [R] qqplot > > carol white <wht_...@yahoo.com> wrote > > >So the conclusion is that abline(0,1) should always be used and if it > doesn't go through the qqplot, the two distributions are not similar? > > I think it depends what you mean by "similar". E.g., if you mean "are both > of these distributions (e.g.) normal?" then abline(0,1) is not always useful. > But if you mean "Do these have the same mean, sd, and distribution?" then > abline(0,1) is the way to go. > > Peter > > Peter L. Flom, PhD > Statistical Consultant > Website: www DOT peterflomconsulting DOT com > Writing; http://www.associatedcontent.com/user/582880/peter_flom.html > Twitter: @peterflom > > ______________________________________________ > 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. ______________________________________________ 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.
