I sent this email before, but I got a r-help-bounce message and I don know 
if it got to the m-list. Sorry if you had already seen it.

I'm using the areg.boot function to do an ace regression. So far I've been 
able to do some simple running tests to fit a model with some input data, 
predict the response with new data, and find the inverse transform of such 
prediction (apparently). The commands I'm using are the following:

library(MASS)
library(Hmisc) 
xyt = read.table("tra100unifxy.dat") #2x100 table of training data (expl. 
variables)
zt = read.table("tra100unifzR.dat") #1x100 table of training data (resp. 
variables)
zs = read.table("sim10000z.dat") #2x10000 table of new data to predict 
(expl. variables)
xys = read.table("sim10000xy.dat") #1x10000 table of expected responses
x = xyt[,1]
y = xyt[,2]
z = zt[,1]
xynew = data.frame(x=xys[,1],y=xys[,2])
ace.r = areg.boot(z ~ x + y, B = 100)
f = Function(ace.r, ytype='inverse')
za = f$z(predict(ace.r,xynew))

I have a couple question:

1.) Is that the correct way of finding the inverse transform for the 
responses?
2.) I'm evaluating the model's goodness of fit using the Fraction of 
Variance Unexplained, which I'm calculating as:

rsa = za - zs
FVUa = sum(rsa*rsa)/(10000*var(zs)) #10000 is the size of the test set

The thing is I'm not getting satisfactory results. Is there a way to improve 
the results of the regression?. At the moment I'm not too confident with the 
formula I'm using as a parameter for areg.boot, since the response variables 
were generated as a substantially more complex function than z = x+y. I 
don't get this formula thing yet and maybe I'm passing a totally unrelated 
formula to the function.

On 9/7/05, Frank E Harrell Jr <f.harrell@vanderbilt.edu> wrote:
> 
> Luis Pineda wrote:
> > Well, I had no idea, since I read this in the documentation:
> >
> > "|x| - for |transace| a numeric matrix. For |areg.boot| |x| may be a
> > numeric matrix or a formula...||"
> >
> > Luis Pineda
> 
> Sorry about that - you are right.
> 
> Thomas - please debug the code to make areg.boot work with x = numeric
> matrix, or correct the help file. Thanks -Frank
> 
> --
> Frank E Harrell Jr Professor and Chair School of Medicine
> Department of Biostatistics Vanderbilt University
>

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