24 March 2014 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
5 March 2013 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
19 February 2013 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
29 April 2011 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers
1 March 2011 | Publisher: United States Congressional Research Service | Document type: Research, Background and Discussion Papers