Thanks. I have been able to create the following simple function to examine the vertical gap between two CDFs at a value along the x-axis that I specify. For example,
I create the ECDFs: >male.ecdf<-ecdf(egmale$math) >female.ecdf<-ecdf(egfemale$math) I then define the following function: >dif.cdf<-function(x){return(abs(female.ecdf(x)-male.ecdf(x)))} Now, I can use the function to measure the gap at values along the x-axis (i.e., gap = F(x)-G(x). Also, the CDFs do not cross at any point): >dif.cdf(0) which returns a value that is the size of the gap at a specific score between males and females. What I would like to be able to do is measure the vertical gap at each point along the x-axis and then plot the gap. This would illustrate for how large differences in student achievement are at different score values into a nice visual display. The brute force way seems to use the function above for each score value. However, this is, of course, inefficient. Any ideas on how I might be able to create a function that would be more efficient? Many thanks, Harold ------ Harold C. Doran Director of Research and Evaluation New American Schools 675 N. Washington Street, Suite 220 Alexandria, Virginia 22314 703.647.1628 -----Original Message----- From: Thomas Lumley [mailto:[EMAIL PROTECTED] Sent: Thursday, February 19, 2004 10:49 AM To: Samuelson, Frank* Cc: [EMAIL PROTECTED] Subject: RE: [R] Area between CDFs On Wed, 18 Feb 2004, Samuelson, Frank* wrote: > > You may not want to integrate cdfs. They're already probabilities. :) > Nice analytic statistics exist for just the maximum distance between > the cdfs, for example. > And for the area between cdfs, which is perhaps better known as the difference in means. -thomas ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html