R help - Apr 2011 - Survival analysis: same subject with multiple treatments

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I need some help to figure out what is the proper model in survival
analysis
for my data.
Subjects were randomized to 3 treatments in trial 1, some of them
experience
the event during the trial;
After period of time those subjects were randomized to 3 treatments
again in
trial 2, but different from what they got in 1st trial, some of them
experience the event during the 2nd trial (I think the carryover effect
can
be ignored since the time between two trials is long enough.)
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If it were me I would add cluster(subject) to the model. Multiple
events/subject is not simple, however, and you should find a book
chapter to read.

Terry Therneau