[R] percent inclusion in cph
sushi4u at libero.it
Tue Nov 13 07:08:07 CET 2007
I have to calculate the percent inclusion of each variable in a bootstrap validation of a cox proportional hazards model(described in Sauerbrei and Schumacher, Stat Med 11:1093, 1992).
First I need to get a bootstrap sample from my dataset, which I did with the sample function. Then I tried to run a cph model and looked which covariates are significant. This I would repeat 200 times and at the end calculate how many percent the covariates were included.
This is what I entered:
boot1 <- sample(Dataset, 300, replace=T)
cph1 <- cph(Surv(months,status) ~ cov1 + cov2 + cov3 + cov4, data=boot1)
Unfortunately, I get exactly the same results (coefficient, SE, p-value) then when I would fit a Cox model without drawing a bootstrap sample before.
How do I do it right? Or is there another way to calculate the percentage?
Sorry for my bad English.
Dott. Mario Rossi
University of Foggia, Italy
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