| Year | Value | | 2022 | 9.765566671644 | | 2021 | 4.787983101236 | | 2020 | 1.767515923567 | | 2019 | 2.7570972756277 | | 2018 | 3.9756101574069 | | 2017 | 3.6024774134894 | | 2016 | 4.0868228057724 | | 2015 | 3.1290027447393 | | 2014 | 5.0288276745677 | | 2013 | 2.6838573871858 | | 2012 | 3.675918979745 | | 2011 | 8.2539682539683 | | 2010 | 4.6511627906976 | | 2009 | 2.5919467343057 | | 2008 | 10.154784648902 | | 2007 | 8.1304741769858 | | 2006 | 9.5893494112923 | | 2005 | 6.8073820311638 | | 2004 | 4.3232649296749 | | 2003 | 14.236797049914 | | 2002 | 10.510242085661 | | 2001 | 7.2680602858483 | | 2000 | 8.9821597675002 | | 1999 | 6.7522658610272 | | 1998 | 11.553268435584 | | 1997 | 6.9495660853412 | | 1996 | 9.7996833901608 | | 1995 | 13.425414364641 | | 1994 | 20.566194837635 | | 1993 | 18.208661417323 | | 1992 | 15.192743764172 | | 1991 | 24.225352112676 | | 1990 | 37.25995617992 | | 1989 | 26.422126723559 | | 1988 | 22.594257178527 | | 1987 | 21.810274035098 | | 1986 | 31.7425972673 | | 1985 | 25.210716435882 | | 1984 | 20.311462546025 | | 1983 | 13.433755563163 | | 1982 | 5.1200654371319 | | 1981 | 12.974697469819 | | 1980 | 22.447330136218 | | 1979 | 28.161038602444 | | 1978 | 10.660247592918 | | 1977 | 9.3598529166284 | | 1976 | 4.474614746645 | | 1975 | 6.6930600836675 | | 1974 | 25.233317779108 | | 1973 | 12.796894532602 | | 1972 | 9.1803749730368 | | 1971 | 4.9532569364099 | | 1970 | 0.85955602100691 | | 1969 | 2.2468475357472 | | 1968 | 0.70807357785437 | | 1967 | 1.3652675922191 | | 1966 | 2.8731942216033 | | 1965 | 3.8592981578052 | | 1964 | 1.3698630136987 | | 1963 | 2.0979020979021 | | 1962 | 1.4184397163121 | | 1961 | 18.487394957983 | | 1960 | 8.181818181818 |
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