I seriously doubt that a survfit object could only contain that
information. I suspect that you are erroneously thinking that what
print.survfit offers is the entire story.
What does str(survfit(<formula>, data=<dataframe>) ) show you?
> data(aml)
> aml.mdl <- survfit(Surv(time, status) ~ x, data=aml)
# this is with survfit.Design since I load Hmisc/Design by default now.
> str(aml.mdl)
List of 18
$ n : int 23
$ time : num [1:20] 9 13 18 23 28 31 34 45 48 161 ...
$ n.risk : num [1:20] 11 10 8 7 6 5 4 3 2 1 ...
$ n.event : num [1:20] 1 1 1 1 0 1 1 0 1 0 ...
$ surv : num [1:20] 0.909 0.818 0.716 0.614 0.614 ...
$ type : chr "right"
$ ntimes.strata: Named int [1:2] 10 10
..- attr(*, "names")= chr [1:2] "1" "2"
$ strata : Named num [1:2] 10 10
..- attr(*, "names")= chr [1:2] "Maintained" "Nonmaintained"
$ strata.all : Named int [1:2] 11 12
..- attr(*, "names")= chr [1:2] "Maintained" "Nonmaintained"
$ std.err : num [1:20] 0.0953 0.1421 0.1951 0.2487 0.2487 ...
$ upper : num [1:20] 0.987 0.951 0.899 0.835 0.835 ...
$ lower : num [1:20] 0.508 0.447 0.35 0.266 0.266 ...
$ conf.type : chr "log-log"
$ conf.int : num 0.95
$ maxtime : num 161
$ units : chr "Day"
$ time.label : chr "time"
$ call : language survfit(formula = Surv(time, status) ~ x,
data = aml)
- attr(*, "class")= chr "survfit"
>
I also don't think survfit returns a Cox model.
On Feb 17, 2009, at 10:37 AM, Bernhard Reinhardt wrote:
Hi!
I came across R just a few days ago since I was looking for a
toolbox for cox-regression.
I´ve read
"Cox Proportional-Hazards Regression for Survival Data
Appendix to An R and S-PLUS Companion to Applied Regression" from
John Fox.
As described therein plotting survival-functions works well
(plot(survfit(model))). But I´d like to do some manipulation with
the survival-functions before plotting them e.g. dividing one
survival-function by another.
survfit() only returns an object of the following structure
n events median 0.9LCL 0.9UCL
55.000 55.000 1.033 0.696 1.637
Can you tell me how I can calculate a survival- or baseline-function
out of these values and how I extract the values from the object? I
´m sure the calculation is done by the corresponding plot-routine,
but I couldn´t find that one either.
Regards
Bernhard
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