. 2011 Jan 6;11:12. doi: 10.1186/1471-2458-11-12
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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (<url>http://creativecommons.org/licenses/by/2.0</url>), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Figure 1.
Study group.