Dear Samuel, The radius reflect the desired coverage of the ellipse. You should be able to use radius <- sqrt(qchisq(.95, 2)), I think.
I hope this helps, John -------------------------------- John Fox, Professor Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > project.org] On Behalf Of Sam Field > Sent: April-13-08 11:47 AM > To: r-help@r-project.org > Subject: [R] plotting muliple CI ellipses for EB estimates > > I have empirical Bayes estimates for slopes and intercepts for a number > of > subjects and I would like to plot the slopes and intercepts with > confidence > ellipses. These ellipses would be based on the confidence intervals for > the > slope and intercepts (forming the major and minor axis of each > ellipse), and > the correlation in the slope and intercepts. > > > The ellipse function in the car library looks like the way to go, the > add= > argument would allow me to over-plot. There are three arguments that > generate > the ellipse. > > center > shape > radius > > Center would be the posterior means for the intercept and slopes. > shape would be the posterior covariance matrices (I think) > > I don't know what I would use for the radius argument however. My guess > would > be the upper bound of a confidence interval for either the slope or the > intercept, but this does not return sensible results. I guess I need to > know > more about the geometry of ellipse, but if anybody can provide any > assistance, > I would really appreciate it. > > > thanks! > > > > -- > ********Note the new contact information******* > > Samuel H. Field, Ph.D. > Senior Research Investigator > CHERP/Division of Internal Medicine - University of Pennsylvania > Philadelphia VA Medical Center > 3900 Woodland Ave (9 East) > Philadelphia, PA 19104 > (215) 823-5800 EXT. 6155 (Office) > (215) 823-6330 (Fax) > > ______________________________________________ > 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.
