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. 2014 Jul 3;15:264. doi: 10.1186/1745-6215-15-264

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Copyright © 2014 Teare et al.; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Distribution of planned RCT study power when using the SD_pestimate derived from the pilot study. The planned study size is used to calculate the true power if SD = 1 is assumed. The graph shown is for a true effect size of 0.2. The vertical axis is true power. The x-axis shows the size of the two-arm pilot study.