Dear Chris,
I took a quick look at your document. You might be interested in
Friendly, Monette, and Fox, Elliptical Insights: Understanding
Statistical Methods through Elliptical Geometry, Statistical Science
2013, 28: 1–39, which is available at
<https://arxiv.org/pdf/1302.4881.pdf>. I probably should cite that paper
in ?car::ellipse.
Best,
John
On 2022-01-15 12:00 p.m., Chris Evans wrote:
This spurred me on to clarify my own understanding of these ellipses (and of
ellipsoid hulls) and led to:
https://www.psyctc.org/Rblog/posts/2022-01-15-data-ellipses-and-confidence-ellipses/
And I am, decidedly nervously, putting it here in case it's useful to you Paul
or
to anyone else. I think I have the basic ideas correct but of course, if any
proper
statisticians have corrections, I would love to receive them, off list probably
unless the errors are terrible. I am entirely self-taught as a statistician,
much
of what I've learned has come from probably over 10, perhaps nearer 20 years on
this
list. Thanks to all for all the work to maintain the list and contribute to it.
Chris
----- Original Message -----
From: "John Fox" <j...@mcmaster.ca>
To: "Paul Bernal" <paulberna...@gmail.com>
Cc: "R" <r-help@r-project.org>
Sent: Friday, 14 January, 2022 18:53:55
Subject: Re: [R] How to create density ellipses with R
Dear Paul,
On 2022-01-14 1:17 p.m., Paul Bernal wrote:
Dear John and R community friends,
To be a little bit more specific, what I need to accomplish is the
creation of a confidence interval ellipse over a scatterplot at
different percentiles. The confidence interval ellipses should be drawn
over the scatterplot.
I'm not sure what you mean. Confidence ellipses are for regression
coefficients and so are on the scale of the coefficients; data
(concentration) ellipses are for and on the scale of the explanatory
variables. As it turns out, for a linear model, the former is the
rescaled 90 degree rotation of the latter.
Because the scatterplot of the (two) variables has the variables on the
axes, a data ellipse but not a confidence ellipse makes sense (i.e., is
in the proper units). Data ellipses are drawn by car::dataEllipse() and
(as explained by Martin Maechler) cluster::ellipsoidPoints(); confidence
ellipses are drawn by car::confidenceEllipse() and the various methods
of ellipse::ellipse().
I hope this helps,
John
Any other guidance will be greatly appreciated.
Cheers,
Paul
El vie, 14 ene 2022 a las 11:27, John Fox (<j...@mcmaster.ca
<mailto:j...@mcmaster.ca>>) escribió:
Dear Paul,
As I understand it, the ellipse package is meant for drawing confidence
ellipses, not density (i.e., data) ellipses. You should be able to use
ellipse::ellipse() to draw a bivariate-normal density ellipse (assuming
that's what you want), but you'll have to do some computation first.
You might find the dataEllipse() function in the car package more
convenient (again assuming that you want bivariate-normal density
contours).
I hope this helps,
John
--
John Fox, Professor Emeritus
McMaster University
Hamilton, Ontario, Canada
web: https://socialsciences.mcmaster.ca/jfox/
<https://socialsciences.mcmaster.ca/jfox/>
On 2022-01-14 10:12 a.m., Paul Bernal wrote:
> Dear R friends,
>
> Happy new year to you all. Not quite sure if this is the proper
place to
> ask about this, so I apologize if it is not, and if it isn´t,
maybe you can
> point me to the right place.
>
> I would like to know if there is any R package that allows me to
produce
> density ellipses. Searching through the net, I came across a
package called
> ellipse, but I'm not sure if this is the one I should use.
>
> Any help and/or guidance will be greatly appreciated.
>
> Best regards,
>
> Paul
>
> [[alternative HTML version deleted]]
>
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