Dear Stephen,
On 2021-05-11 10:20 a.m., Stephen Ellison wrote:
>> In doing meta-analysis of diagnostic accuracy I produce ellipses of confidence >> and prediction intervals in two dimensions. How can I calculate the area of >> the ellipse in ggplot2 or base R? > > There are established formulae for ellipse area, but I am curious: in a 2-d ellipse with different quantities (eg coefficients for salary and age) represented by the different dimensions, what does 'area' mean? I answered James's question narrowly, but the point you raise is correct -- the area isn't directly interpretable unless the coefficients are measured in the same units. It still may be possible to compare areas of ellipsoids for, say, different regressions with the same predictors, as ratios, however, since these ratios would be unaffected by rescaling the coefficients. The generalization of this idea to ellipsoids of any dimension is the basis for the generalized variance-inflation factors computed by the vif() function in the car package. Best, John John Fox, Professor Emeritus McMaster University Hamilton, Ontario, Canada web: https://socialsciences.mcmaster.ca/jfox/ > > S > > > ******************************************************************* > This email and any attachments are confidential. Any use...{{dropped:8}} > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. >