[S] Comparing two survival curves with very high survival rates out

Fri, 26 Jun 1998 11:00:50 -0400

dear S-News,

Suppose there is a medical device, call it xyq.
There is to be an undetermined number of patients
enrolled in the study which will last roughly 8 years.
Half the patients will get drug A, half will get drug B, roughly.
It is desired to show that device xyq last longer in patients
on drug A than in patients on drug B.
So there will be a survival curve for xyq in patients on A
and a survival curve for xyq in patients on B.

The problem is that based on past experience, the survival curves for both
A and B will
hover around 95 percent from the start of the study through 5 years. Only
after 5 years do
the survival curves begin to lower and separate noticably.
This is compounded by the fact that between 5 and 8 years we expect
30% or more of the patients to be lost to follow up.

Any ideas for sample size calculations that don't result in enrolling
100,000 patients?
Any ideas for comparing the two survival curves in a case like this?
Any ideas how to do either in SPlus? Literature references?

A substantial part of the study is already handled in Splus,
so it would be ideal to carry out the rest in Splus as well.

Kind regards,
Eric Gibson
Novartis Pharmaceuticals

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