Release of data from an ongoing randomized clinical trial for sample size adjustment or planning

The determination of an appropriate sample size is a key issue in planning and designing randomized clinical trials. In settings with time‐to‐event or binary outcomes, the required sample size depends on the control‐arm event (response) rate. An accurate estimate of this rate is not often available at the planning stage. Therefore, non‐comparative control‐arm or pooled‐arm event rates from an ongoing trial are sometimes released for sample size adjustment or planning purposes. It is shown that such non‐comparative data release may still contain information on the relative treatment benefit and may thus adversely affect the ongoing trial. A simple approach to minimizing the effect of the data release is suggested. Published in 2007 by John Wiley & Sons, Ltd.