changing plot symbol and/or size in plot(cox.zph)

Is there a way to make the

plot(cox.zph(model))

use some other symbol than open circles?

Yes, but after looking at the code, the points call does not have  
trailing "..." so, not without modifying the function:

library(survival)
methods(plot)
getAnywhere(plot.cox.zph)

Now just hack the function:

plot.cox.zph
<gives you the function arguent list and body.

plot.cox.zph2 <-  <insert arguments and code here>

And change these lines:

+         if (resid)
+             points(xx, y)
+         lines(pred.x, yhat)

  to

+         if (resid)
+             points(xx, y, ...)
+         lines(pred.x, yhat)


Then using the example in help(cox.zph) :
plot.cox.zph2(temp, pch=4)  gives you "x"'s instead of "o"'s

--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT