Defining reference category for a cph model summary inside of a "for" loop

I have the following code.

f <- cph(formula = Surv(TimeToDeath, Dead == "Yes")

~1,data=single.dat, x=T, y=T, surv=T)

for(i in c('A', 'B', 'C', 'D', 'E', 'F')){

f <-update(f,as.formula(paste('Surv(TimeToDeath, Dead ==

"Yes")~',i,sep='')))

print(summary(f, paste(i,"=1st Quartile", sep='')))

There is no error message generated in R, but R ignores the reference
category defined with paste in the summary function for the cph model. 

 

The output uses the "1st Quartile" as the reference category to
calculate hazards for some of the variables defined by i, but not all of
them. 

 

 

Any help would be greatly appreciated. 

 

thanks

 

Brian J. Wells, MD, MS

Research Associate

Quantitative Health Sciences

Cleveland Clinic

 

 


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