| Year | Value | | 2018 | 3.842515754 | | 2017 | 3.842515754 | | 2016 | 3.595603574 | | 2015 | 3.69158478 | | 2014 | 3.235068 | | 2013 | 3.077352 | | 2012 | 3.0246638572357 | | 2011 | 2.8184697918906 | | 2010 | 2.546 | | 2009 | 0.723 | | 2008 | 0.831 | | 2007 | 0.876 | | 2006 | 0.828 | | 2005 | 0.797 | | 2004 | 0.771 | | 2003 | 0.659 | | 2002 | 1.086 | | 2001 | 0.978 | | 2000 | 1.043 | | 1999 | 1.2999999523 | | 1998 | 1.7000000477 | | 1997 | 1.7000000477 | | 1996 | 1.7000000477 | | 1995 | 1.6000000238 | | 1994 | 1.2999999523 | | 1993 | 1.2000000477 | | 1983 | 0.1000000015 | | 1981 | 0.200000003 | | 1980 | 0.1000000015 |
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