From: Adaikalavan Ramasamy <ramasamy_at_cancer.org.uk>

Date: Wed 03 Aug 2005 - 20:13:29 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Aug 03 20:20:26 2005

Date: Wed 03 Aug 2005 - 20:13:29 EST

Also see function rocdemo.sca in the ROC package.

The area under the 45 degree line in an ROC curve has an area of 0.5.

Regards, Adai

On Tue, 2005-08-02 at 09:24 -0400, Ravi Varadhan wrote:

*> Hi,
**>
*

> To find the area lying between the curve y = y(x) and 45 degree line (which,

*> assuming it goes through the origin, is y = x), you can use the following
**> function based on trapezoidal rule:
**>
**> trap.rule <- function(x,f) {sum(diff(x)*(f[-1]+f[-length(f)]))/2}
**>
**> trap.rule(x,f=y-x)
**>
**> This area will be negative if y(x) is below the 45 degree line.
**>
**> However, your question is not complete, I think. You need to specify the
**> interval of integration. For this you may need to determine the points of
**> intersection of the two curves, which involves the solution of a fixed point
**> problem.
**>
**> Hope this helps,
**> Ravi.
**>
**> > -----Original Message-----
**> > From: r-help-bounces@stat.math.ethz.ch [mailto:r-help-
**> > bounces@stat.math.ethz.ch] On Behalf Of Renuka Sane
**> > Sent: Tuesday, August 02, 2005 8:51 AM
**> > To: r-help@stat.math.ethz.ch
**> > Subject: [R] question on graphs and finding area under a curve
**> >
**> > Question on graphs:
**> >
**> > The default case for drawing a graph in R, is where a little space is left
**> > on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) -
**> > -
**> > there will be some space between the edge of the x-axis and where 0 is
**> > placed. If I want 0 on the edge, how do I do it in R?
**> >
**> > Area under the curve:
**> >
**> > I have a 45 degree line and a curve above or below it. Is there a way in R
**> > to find the area between the two?
**> >
**> > Thanks,
**> > Renuka
**> >
**> > --
**> > Renuka Sane
**> > http://www.nyx.net/~rsane
**> >
**> > [[alternative HTML version deleted]]
**> >
**> > ______________________________________________
**> > R-help@stat.math.ethz.ch mailing list
**> > https://stat.ethz.ch/mailman/listinfo/r-help
**> > PLEASE do read the posting guide! http://www.R-project.org/posting-
**> > guide.html
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
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**> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
*

>

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Aug 03 20:20:26 2005

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