| Year | Value | | 2022 | 8.6409110897385 | | 2021 | 4.2593641754287 | | 2020 | 2.9402951426397 | | 2019 | 2.6432819271956 | | 2018 | 3.1983464156241 | | 2017 | 3.3969758489525 | | 2016 | 2.8217078474766 | | 2015 | 3.1578311798092 | | 2014 | 3.5256620375828 | | 2013 | 4.3433713127952 | | 2012 | 5.0085254625088 | | 2011 | 5.7967680920653 | | 2010 | 4.0430625878884 | | 2009 | 4.2025166121648 | | 2008 | 10.287684792119 | | 2007 | 6.1606866937373 | | 2006 | 6.0991424767729 | | 2005 | 6.0147582262775 | | 2004 | 4.4749928907811 | | 2003 | 4.5469001211872 | | 2002 | 4.022881937116 | | 2001 | 5.077450455225 | | 2000 | 4.1992882562281 | | 1999 | 4.5670875285674 | | 1998 | 6.8456698080724 | | 1997 | 7.1064724273089 | | 1996 | 8.8640874157751 | | 1995 | 11.669614643249 | | 1994 | 21.147770860727 | | 1993 | 10.748646716372 | | 1992 | 10.098967153517 | | 1991 | 12.615315382885 | | 1990 | 11.064425770308 | | 1989 | 9.012995945555 | | 1988 | 8.9830033820899 | | 1987 | 8.2258064516129 | | 1986 | 8.7316399570467 | | 1985 | 8.7994377663954 | | 1984 | 10.369566518164 | | 1983 | 10.636303676138 | | 1982 | 10.825749167569 | | 1981 | 12.974697469819 |
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