Tom: You asked whether two groups have the same underlying population 1st and 2nd moments. The answer is: no they don't. Nothing is ever exactly the same as anything else (indeed, I think this is the Paul Exclusion Principle ;-) ).
So quoting Jim Holtman: "What is the question?" That certainly requires someone who knows something about the scientific issues (not me!). But maybe it's something like: "Well, if these two **populations** are more different than a, b, c, ... in population characteristics A, B, and C,... then that is scientifically meaningful." So then you can ask: "Well how can I measure/statistically characterize A,B, and C,...? -- How much uncertainty will there be in this characterization (depends on study design and how one characterizes "uncertainty" ) and how much can I tolerate and still reach scientifically useful conclusions." And so forth... all of which might be squeezed into Bayesian, or classical, parametric, nonparametric, or whatever holes happen to satisfy your particular "religious" convictions. Or, perhaps even better, be informed by some good plots (horrors -- no P-Values! ... but those are **my** religious convictions). But those are mere statistical details, about which all I can safely say is: The question is not "Are they the same?" Cheers, Bert Gunter Genentech Nonclinical Biostatistics P.S. Technical comment (because, alas, I **are** a statistician): You probably want the ellipsoids you speak of to cover subsets of the **populations** with some degree of certainty, not of the **data.** Disclaimer: Bert Gunter's opinions only. Associate neither my company nor my colleagues with my obstreperousness. -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Tom La Bone Sent: Monday, March 29, 2010 9:56 AM To: r-help@r-project.org Subject: Re: [R] Ellipse that Contains 95% of the Observed Data I know what "get a bigger sample means". I have no clue what "ask a more statistically meaningful question" means. Can you elaborate a bit? Tom -- View this message in context: http://n4.nabble.com/Ellipse-that-Contains-95-of-the-Observed-Data-tp1694538 p1695357.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.