| Year | Value | | 2022 | 8.4873086953504 | | 2021 | 4.2227896203322 | | 2020 | 2.96354992076 | | 2019 | 2.741763824758 | | 2018 | 3.2380155894772 | | 2017 | 3.6470465668627 | | 2016 | 2.9524954121456 | | 2015 | 3.1634645736588 | | 2014 | 3.5892201661666 | | 2013 | 4.698320122543 | | 2012 | 5.0141146428186 | | 2011 | 6.1074271459025 | | 2010 | 4.1567272268017 | | 2009 | 4.2107735664055 | | 2008 | 10.445557944655 | | 2007 | 6.311934592934 | | 2006 | 6.0991424767729 | | 2005 | 6.4212964821989 | | 2004 | 4.6884088484314 | | 2003 | 5.1289949942242 | | 2002 | 4.2687093230911 | | 2001 | 5.1672399608334 | | 2000 | 4.1654044229028 | | 1999 | 4.6807630054302 | | 1998 | 7.1463266545233 | | 1997 | 7.1253272251306 | | 1996 | 9.2204666237699 | | 1995 | 12.316084888597 | | 1994 | 21.729346883819 | | 1993 | 10.263099825652 | | 1992 | 10.056116744884 | | 1991 | 12.445244163387 | | 1990 | 10.653505786249 | | 1989 | 8.8468869123255 | | 1988 | 8.9830033820899 | | 1987 | 8.1523425380087 | | 1986 | 8.7316399570467 | | 1985 | 9.0905011888749 | | 1984 | 10.284098213138 | | 1983 | 10.620753648024 | | 1982 | 10.831809773817 | | 1981 | 12.857207792164 |
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