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. 2010 Aug 16;5(8):e12203. doi: 10.1371/journal.pone.0012203

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This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

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Papers from journals included in the Science Citation Index and the Social Sciences Citation Index were enumerated. Each region received a fractional count based on the fraction of the institutions in the region.