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. Author manuscript; available in PMC: 2012 May 8.
Published in final edited form as: Methods Rep RTI Press. 2010 Sep 1;19(1009):1–14. doi: 10.3768/rtipress.2010.mr.0019.1009

  • 1 to 4

  • 5 to 24

  • 25 to 99

  • 100 to 499

  • 500 to 4,999

  • 5,000 or greater