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:

[hidden email] [mailto:

[hidden email]] On

Behalf Of Tom La Bone

Sent: Monday, March 29, 2010 9:56 AM

To:

[hidden email]
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-tp1694538p1695357.html

Sent from the R help mailing list archive at Nabble.com.

______________________________________________

[hidden email] mailing list

https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide

http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.

______________________________________________

[hidden email] mailing list

https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide

http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.