| Year | Value | | 2021 | 0.026099 | | 2020 | 0.024731 | | 2019 | 0.031566 | | 2018 | 0.066817 | | 2009 | 23.105 | | 2008 | 25.522 | | 2007 | 26.095 | | 2006 | 29.001 | | 2005 | 24.399 | | 2004 | 22.825 | | 2003 | 20.254 | | 2002 | 42.717 | | 2001 | 36.88 | | 2000 | 42.03 | | 1999 | 46.5 | | 1998 | 51.5999984741 | | 1997 | 34.4000015259 | | 1996 | 41.5999984741 | | 1995 | 38.9000015259 | | 1994 | 25 | | 1993 | 21.7000007629 | | 1992 | 9.3000001907 | | 1991 | 9.6000003815 | | 1990 | 13.1000003815 | | 1989 | 19.1000003815 | | 1988 | 38.2999992371 | | 1987 | 36.7000007629 | | 1986 | 34.7999992371 | | 1985 | 56.9000015259 | | 1984 | 55.5 | | 1983 | 43.5 | | 1982 | 45.7000007629 | | 1981 | 31.3999996185 | | 1980 | 27.7000007629 | | 1979 | 8.1999998093 | | 1978 | 7.8000001907 | | 1977 | 5.8000001907 | | 1976 | 5.6999998093 | | 1975 | 8.5 | | 1974 | 8.3000001907 | | 1973 | 7.4000000954 | | 1972 | 4.3000001907 | | 1971 | 6.8000001907 | | 1970 | 5.9000000954 |
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