| Year | Value | | 2014 | 5.6436513524702 | | 2013 | 6.0346862506444 | | 2012 | 5.0755564937676 | | 2011 | 5.4663145275306 | | 2010 | 6.0385922082679 | | 2009 | 5.4571077731104 | | 2008 | 3.6680226492701 | | 2007 | 3.2805213698945 | | 2006 | 3.2259744730464 | | 2005 | 3.6564706783208 | | 2004 | 4.6114776396626 | | 2003 | 4.6923062672293 | | 2002 | 4.8755318053448 | | 2001 | 5.6121055234052 | | 2000 | 8.3237222448449 | | 1999 | 7.6695379976034 | | 1998 | 8.6297212098485 | | 1997 | 6.7590614806352 |
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