[R] OT Futility Analysis

[Kevin E. Thorpe]

I beg your pardon if this is too off topic.  I am posting here
since I hope to find an R solution to my problem.  Please indulge
me while I give a little background about what I'm trying to do.

I'm on a DSMB for a clinical trial.  The Steering Committee for the
trial has asked us to perform a futility analysis on their primary
outcome which is a time-to-event endpoint.  The trial was not designed
with group sequential methods, nor was any futility analysis spelled
out in the protocol.  Another thing which may be relevant is that
due to circumstances beyond the investigators' control, the trial
will stop recruitment prematurely unless there is some compelling
reason for them to find a way to continue the trial.  Lastly, the
trial has accrued not quite half of the planned sample size.

Admittedly, I don't have a vast amount of experience implementing
stopping rules.  In other protocols I have seen where futility
analyses have been planned but a group sequential design has not
otherwise been employed, conditional power has been used for the
futility rule.  So naturally, that was my first thought (although
I may well be wrong) in this case.  I have done RSiteSearch() with
the following terms (three different searches):

	futility analysis
	conditional power
	stochastic curtailment

Nothing that looked relevant to my problem jumped out at me.

I have read, somewhat recently, that there are problems with conditional
power, although I don't remember the details at the moment.  This
has prompted me to consider other approaches to the problem.

One simple thing that has occurred to me, although I don't know
what the implications are is to simply look at a confidence
interval around the hazard ratio for the treatment effect.  In
the event that the CI includes 1 and excludes any clinically
important difference, I would take that as an indication of
futility.

I would appreciate your comments on this and to learn of any more
formal methods, particularly of implementations in R.

Thank you for reading.

Kevin

-- 
Kevin E. Thorpe
Biostatistician/Trialist, Knowledge Translation Program
Assistant Professor, Department of Public Health Sciences
Faculty of Medicine, University of Toronto
email: kevin.thorpe at utoronto.ca  Tel: 416.946.8081  Fax: 416.946.3297