[R] Comparing two different 'survival' events for the same subject using survdiff?

[Terry Therneau]

-----Original Message-----

I have a dataset which for the sake of simplicity has two endpoints. We would like to test 
if two different end-points have the same eventual meaning. To try and take an example 
that people might understand better:

Lets assume we had a group of subjects who all received a treatment. The could stop 
treatment for any reason (side effects, treatment stops working etc). Getting that data is 
very easy. Measuring if treatment stops working is very hard to capture... so we would 
like to test if duration on treatment (easy) is the same as time to treatment failure (hard).

--- End ----

The problem you describe is known as "surrogate endpoints" and addressing it is harder 
than you think. You will need to look in the literature to gain an understanding of the 
issues before you proceed. Your question is an important one and lots of folks have 
thought about it more deeply than I.

Cohn JN (2004). "Introduction to Surrogate Markers". Circulation (American Heart 
Association) 109 (25 Suppl 1): IV20–1. doi:10.1161/01.CIR.0000133441.05780.1d

Fleming T, David D. Surrogate End Points in Clinical Trials: Are We Being Misled? Ann 
Intern Med. 1996 Oct 1;125(7):605-13

Terry T.