Thanks for all your replies. I just wanted to compare the distributions of two populations and see how different they are. I thought that QQplot would be a good idea. It's true that the mean and sd of the two distributions are not the same. I don't know if any other method or graphical presentation like five number, mean and sd as suggested, or boxplot would have been more suited to be used.
thanks for your advices, --- On Mon, 11/2/09, John Fox <j...@mcmaster.ca> wrote: > From: John Fox <j...@mcmaster.ca> > Subject: RE: [R] qqplot > To: "'Peter Flom'" <peterflomconsult...@mindspring.com> > Cc: r-h...@stat.math.ethz.ch, "'carol white'" <wht_...@yahoo.com>, "'Yihui > Xie'" <xieyi...@gmail.com> > Date: Monday, November 2, 2009, 9:24 AM > 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.
