[Rd] Possible bug in summary.survfit - 'scale' argument ignored?

[Marc Schwartz]

Hi all,

Using:

   R version 2.8.1 Patched (2009-03-07 r48068)

on OSX (10.5.6) with survival version:

   Version:            2.35-3
   Date:               2009-02-10


I get the following using the first example in ?summary.survfit:

 > summary( survfit( Surv(futime, fustat)~1, data=ovarian))
Call: survfit(formula = Surv(futime, fustat) ~ 1, data = ovarian)

  time n.risk n.event survival std.err lower 95% CI upper 95% CI
    59     26       1    0.962  0.0377        0.890        1.000
   115     25       1    0.923  0.0523        0.826        1.000
   156     24       1    0.885  0.0627        0.770        1.000
   268     23       1    0.846  0.0708        0.718        0.997
   329     22       1    0.808  0.0773        0.670        0.974
   353     21       1    0.769  0.0826        0.623        0.949
   365     20       1    0.731  0.0870        0.579        0.923
   431     17       1    0.688  0.0919        0.529        0.894
   464     15       1    0.642  0.0965        0.478        0.862
   475     14       1    0.596  0.0999        0.429        0.828
   563     12       1    0.546  0.1032        0.377        0.791
   638     11       1    0.497  0.1051        0.328        0.752


 > summary( survfit( Surv(futime, fustat)~1, data=ovarian), scale =  
365.25)
Call: survfit(formula = Surv(futime, fustat) ~ 1, data = ovarian)

  time n.risk n.event survival std.err lower 95% CI upper 95% CI
    59     26       1    0.962  0.0377        0.890        1.000
   115     25       1    0.923  0.0523        0.826        1.000
   156     24       1    0.885  0.0627        0.770        1.000
   268     23       1    0.846  0.0708        0.718        0.997
   329     22       1    0.808  0.0773        0.670        0.974
   353     21       1    0.769  0.0826        0.623        0.949
   365     20       1    0.731  0.0870        0.579        0.923
   431     17       1    0.688  0.0919        0.529        0.894
   464     15       1    0.642  0.0965        0.478        0.862
   475     14       1    0.596  0.0999        0.429        0.828
   563     12       1    0.546  0.1032        0.377        0.791
   638     11       1    0.497  0.1051        0.328        0.752

Of course the time periods in the second output should be scaled to  
years, that is (time / 365.25).

I noted this today running some Sweave code, but not sure when the  
actual change in behavior occurred.  I can replicate the same behavior  
on a Windows machine here as well, so this is not OSX specific.

Regards,

Marc Schwartz