| Year | Value | | 2021 | 25.8138525 | | 2019 | 0.0755 | | 2018 | 0.85847 | | 2017 | 5.6883385341 | | 2016 | 5.1483685301 | | 2015 | 7.445320262833 | | 2014 | 11.895 | | 2013 | 12.415236 | | 2012 | 23.544533756747 | | 2011 | 22.718168262535 | | 2010 | 14.638193367 | | 2009 | 41.803 | | 2008 | 46.821 | | 2007 | 45.892 | | 2006 | 51.04 | | 2005 | 43.118 | | 2004 | 40.474 | | 2003 | 36.254 | | 2002 | 32.837 | | 2001 | 32.648 | | 2000 | 36.505 | | 1999 | 33.9000015259 | | 1998 | 16.5 | | 1997 | 23.1000003815 | | 1996 | 46.2999992371 | | 1995 | 52.5999984741 | | 1994 | 39.0999984741 | | 1993 | 36.9000015259 | | 1992 | 34.5999984741 | | 1991 | 11.3000001907 | | 1990 | 12.8999996185 | | 1989 | 17 | | 1988 | 11.8000001907 | | 1987 | 21.6000003815 | | 1986 | 16.2000007629 | | 1985 | 7.3000001907 | | 1984 | 7.6999998093 | | 1983 | 7 | | 1982 | 6 | | 1981 | 5.4000000954 | | 1980 | 12.1000003815 | | 1979 | 11.6000003815 | | 1978 | 10.6999998093 | | 1977 | 10.1000003815 | | 1976 | 9 | | 1975 | 7.1999998093 | | 1974 | 6.9000000954 | | 1973 | 4.1999998093 | | 1972 | 1.7000000477 | | 1971 | 1.7000000477 | | 1970 | 1.7999999523 |
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