To describe a method using confidence intervals (CIs) to estimate the sample size for a pilot randomized trial.
Using one-sided CIs and the estimated effect size that would be sought in a large trial, we calculated the sample size needed for pilot trials.
Using an 80% one-sided CI, we estimated that a pilot trial should have at least 9% of the sample size of the main planned trial.
Using the estimated effect size difference for the main trial and using a one-sided CI, this allows us to calculate a sample size for a pilot trial, which will make its results more useful than at present.
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Published online: November 29, 2012
Accepted: September 5, 2012
Conflict of interest statement: We confirm that we have no conflict of interest.
Competing interests: Both authors have no competing interests.
© 2013 Elsevier Inc. Published by Elsevier Inc. All rights reserved.