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. 2014 May 26;14:506. doi: 10.1186/1471-2458-14-506

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Copyright © 2014 Roos 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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Sibling - neighborhood designs. Within each family, siblings a and b are compared. Within each neighborhood, the two appropriate families are compared: the two sibling a’s with each other and the two sibling b’s with each other.