remove var from model object

[Russell.Ivory@MerrickBank.com]

I have a model

testmodel <- lrm(depvar ~ age+fscore+accts+lates+stage)

As part of my diagnostics I want to manipulate things one continuous measure at a time.  I want to write a function to run a new model that will in short look for linearity.  I have the steps of my function down but I'm having trouble manipulating the model arguments in the function call.

I'd like to have the aruments be very simple as

function(testmodel,indvar)

where testmodel is the existing model object and indvar is the variable in question that I will pull out and manipulate.  For example, if I were looking at age in the model above, the function call would look like

function(testmodel,age)

and the model would then become lrm(depvar ~ age +fscore+accts+lates+stage - age + agemanipulated)

In other words, I would pull age out of the existing model and plug in a manipulated version of age then re-run the model.

I've tried to simply pull age out as a first step with things like

modelvars <- depvar ~ age+fscore+accts+lates+stage
> modelvars
depvar ~ age+fscore+accts+lates+stage
as.formula(paste("lrm(",modelvars,"-age)"))

or

paste("lrm(", substring(testmodel$call, 1, max(nchar(testmodel$call)))[2], "-age)")
[1] "lrm( depvar ~ age+fscore+accts+lates+stage -age)"

but to no avail.

I'm sure the solution is simple, but I cannot find it.  Any pointers would be greatly appreciated.

Russell Ivory
Senior Risk Scoring Analyst
Merrick Bank
10705 South Jordan Gateway
Suite 200
South Jordan, Ut  84095
(801) 545-6640

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