| Year | Value | | 2017 | 8.65 | | 2016 | 8.121949323 | | 2015 | 7.615974662 | | 2014 | 7.11 | | 2013 | 6.6 | | 2012 | 6.106695024 | | 2011 | 5.6 | | 2010 | 5 | | 2009 | 4.5 | | 2008 | 4.287509903 | | 2007 | 2.759704374 | | 2006 | 2.007990079 | | 2005 | 1.46342006 | | 2004 | 1.07750493 | | 2003 | 0.460014187 | | 2002 | 0.157249517 | | 2001 | 0.032223616 | | 2000 | 0.026354732 | | 1999 | 0.016791049 | | 1998 | 0.003415143 | | 1997 | 0.003469104 | | 1996 | 0.00352686 |
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