Date: Wed, 24 Jun 2009 11:21:30 -0500
Reply-To: Herbert Morley A <Morley.Herbert@HCAHEALTHCARE.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Herbert Morley A <Morley.Herbert@HCAHEALTHCARE.COM>
Subject: Sample Size by Simulation
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A number of times I have come across people suggesting that the use of a simulation to determine an appropriate sample size. Generally I would use the SAS procedure Proc Power for the appropriate data structure, or look it up in tables.
The current problem. The docs want to do a trial where they are comparing two types of treatment for a piece of vein. They are looking for a non-inferiority outcome. Historically treatment A has a failure rate of 20%. Because treatment B has benefits for the patient, they will accept a failure of 24% (20% worse) as an acceptable outcome. Worse than that, the tradeoff would make it a no-go. These are yes/no outcomes.
How would I do a simulation to get the sample size for power = 0.8 (say). I am looking for the steps, rather than the actual code, which I probably could handle.
I tried a uniform random number generation with a divide at 0.2 to create a dataset with the desired proportion of yes/no's. I then ran a bootstrap to get samples and then calcluated the mean and CI for the distribution. Is this the right path? If so, now what. If not, what should I be doing?
Thanks in advance for any hints.
Biomedical and Surgical Research
Medical City Dallas Hospital
7777 Forest Lane, Ste C-740
Dallas, TX 75230