[R] rpart for survival fits

[Terry Therneau]

> When I plot a survival fit using rpart for the classification tree, for each
> node, there is a decimal based number above the event/total. I tried to see if
> it's the exponential ratio or logrithmics, neither seem to be the case. I'm
> wondering if anyone knows what they are.

---------
 
  It is an estimate of the event rate, using a Baysian shrinkage argument
  	(#events +a) / (n +b)  *c
 
To understand how the constants a and b are chosen, you need to read the 
detailed documentation (as pointed out already by Brian R).  The constant c is 
chosen to make the printed "rate" of the top node equal to 1.  This last is done 
just to make it easier to scan the tree -- one can easily see that the rate is, 
say, 20% lower in some particular node than for the data set as a whole.


	Terry Therneau