Dear Jeff,
I don't think that it would be sensible to claim that it *never* makes
sense to multiply quantities measured in different units, but rather
that this would rarely make sense for regression coefficients. James
might have a justification for finding the area, but it is still, I
think
Dear Stephen
In that application the axes would be sensitivity and specificity (or
their inverses) or some transformation of them like logits so the units
would be the same. Whether the area has any scientific meaning I am not
sure.
Michael
On 11/05/2021 15:20, Stephen Ellison wrote:
In do
The area is a product, not a ratio. There are certainly examples out there of
meaningful products of different units, such as distance * force (work) or
power " time (work).
If you choose to form a ratio with the area as numerator, you could conceivably
obtain the numerator with force snd dista
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 formul
> 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 qu
Hi John,
Thanks for that. An education for me and my advice to use "str" to
check for the radii in the return value
was clearly mistaken.
Jim
On Sat, May 8, 2021 at 2:15 AM John Fox wrote:
>
> Dear David and Jim,
>
> As I explained yesterday, a confidence ellipse is based on a quadratic
> form
Dear David and Jim,
As I explained yesterday, a confidence ellipse is based on a quadratic
form in the inverse of the covariance matrix of the estimated
coefficients. When the coefficients are uncorrelated, the axes of the
ellipse are parallel to the parameter axes, and the radii of the ellips
On 5/6/21 6:29 PM, Jim Lemon wrote:
Hi James,
If the result contains the major (a) and minor (b) axes of the
ellipse, it's easy:
area<-pi*a*b
ITYM semi-major and semi-minor axes.
--
David
try using str() on the result you get.
Jim
On Fri, May 7, 2021 at 3:51 AM james meyer wrote:
Hi James,
If the result contains the major (a) and minor (b) axes of the
ellipse, it's easy:
area<-pi*a*b
try using str() on the result you get.
Jim
On Fri, May 7, 2021 at 3:51 AM james meyer wrote:
>
> In doing meta-analysis of diagnostic accuracy I produce ellipses of confidence
> and predic
Dear James,
To mix notation a bit, presumably the (border of the) confidence ellipse
is of the form (b - beta)'V(b)^-1 (b - beta) = c, where V(b) is the
covariance matrix of b and c is a constant. Then the area of the ellipse
is pi*c^2*sqrt(det(V(b))). It shouldn't be hard to translate that in
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?
thank you
James Meyer
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