18 March 2014 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
4 March 2011 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
18 February 2011 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
21 December 2010 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers