| Year | Value | | 2021 | 0.168685 | | 2020 | 1.37475 | | 2019 | 7.38543 | | 2018 | 7.819001 | | 2017 | 8.36736 | | 2016 | 8.0220338432557 | | 2015 | 7.843989 | | 2014 | 13.211711025 | | 2013 | 8.869308 | | 2012 | 9.4936112384425 | | 2011 | 7.1494981276749 | | 2010 | 3.900821 | | 2009 | 2.562 | | 2008 | 5.927 | | 2007 | 5.364 | | 2006 | 6.34 | | 2005 | 6.069 | | 2004 | 6.324 | | 2003 | 7.583 | | 2002 | 8.184 | | 2001 | 7.388 | | 2000 | 8.441 | | 1999 | 8.3999996185 | | 1998 | 7.4000000954 | | 1997 | 0.8000000119 | | 1996 | 3.2999999523 | | 1995 | 3.2000000477 | | 1994 | 3 | | 1993 | 3 | | 1992 | 1.3999999762 | | 1991 | 1.2000000477 |
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