Dear R users,

I have a question concerning the nltm package. Before posting to the R list I first contacted the author of the package twice but no succes. May be I've got the wrong email!  My question is about the object "surv" given in the package "nltm". As explained, the object "surv" represents the MLE estimates of the baseline survival function evaluated at the estimated profile likelihood parameters.  When I extracted this baseline survival function using "surv"  I was surprised by the fact that almost all its values are close to 1. I thought  maybe because It is a simulated example. So I used the same example provided in the package using the PH family in "nltm.model" and then I compared the estimated baseline survival with the one provided by the usual coxph package. As a result, the parameters theta are similar as expected BUT the estimated baseline survivals  are completely different. Am missing something here? I would be really very grateful if anyone can let me know where I am wrong. The examples are as follows:

# fit a Cox PH  Model using nltm package
data(melanoma)
fit.nltm <- nltm(Surv(time,status) ~ size + age, data=melanoma, nlt.model="PH")
surv.nltm <- fit.nltm$surv
# fit a Cox PH model using coxph package
data(melanoma)
fit.coxph <- coxph(Surv(time,status) ~ size + age, data=melanoma)
surv.coxph <- summary(survfit(fit.coxph))[[1]]

The finite-dimension parameters theta in fit.nltm and fit.coxph are similar but as you can see "surv.nltm" and "surv.coxph" are completey different. Furthermore,  "fit.nltm"  have all values close to 1.

All the bests

Abderrahim

	[[alternative HTML version deleted]]


