| Year | Value | | 2020 | 1.8120452246953 | | 2019 | 3.0150787559178 | | 2018 | 2.9525937221301 | | 2017 | 3.4901588865118 | | 2016 | 3.6235387771376 | | 2015 | 3.7007324066903 | | 2014 | 3.7270550158219 | | 2013 | 4.195231735009 | | 2012 | 4.4961583541255 | | 2011 | 4.7965953263249 | | 2010 | 4.5528832676643 | | 2009 | 3.9317106542602 | | 2008 | 1.5136327588775 | | 2007 | 0.83389321359717 | | 2006 | 0.84035095032982 | | 2005 | 0.46668048271355 | | 2004 | 0.48749441412651 | | 2003 | 2.4471850406967 | | 2002 | 2.4385971400946 | | 2000 | 8.7131390651847 | | 1999 | 8.8052895135166 | | 1998 | 9.1266232269823 | | 1997 | 10.117745558746 | | 1996 | 10.45557295443 | | 1995 | 9.662676712823 | | 1994 | 1.1991909458419 | | 1993 | 1.3166244907955 | | 1992 | 1.5227122686281 | | 1991 | 1.7023008676817 |
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