Warning trying to plot -log(log(survival))

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of John Sorkin
Sent: Monday, May 11, 2009 12:19 PM
To: r-help at stat.math.ethz.ch
Subject: [R] Warning trying to plot -log(log(survival))

windows xp
R 2.8.1

I am trying to plot the -log(log(survival)) to visually test the
proportional hazards assumption of a Cox regression. The plot, which
should give two lines (one for each treatment) gives only one line and
a warning message. I would appreciate help getting two lines, and an
explanation of the warning message. My problem may the that I have

few events in one of my strata, but I don't know.
Thanks,
John

fit0<-coxph(Surv(Time30,Died)~strata(Rx)+Age,data=GVHDdata)
plot(survfit(fit0),fun="cloglog")


WARNING: Warning in xy.coords (x, y, xlabel, ylabel, log)  :
 2 x values <=0 omitted from logarithmic plot

print(survfit(fit0),fun="cloglog")

Call: survfit.coxph(object = fit0)

      n events median 0.95LCL 0.95UCL
Rx=0 31      5    Inf     Inf     Inf
Rx=1 32     15    Inf    1.17     Inf

John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center 10 North Greene Street GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)

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