| Year | Value | | 2021 | 0.00012 | | 2020 | 0.000643636 | | 2019 | 0.0273 | | 2018 | 0.107366 | | 2017 | 0.546373 | | 2016 | 0.63203 | | 2015 | 0.45552 | | 2014 | 0.09123 | | 2012 | 3.7122254448016 | | 2011 | 4.1867986660175 | | 2010 | 4.090865359 | | 1999 | 2.5999999046 | | 1998 | 2.5 | | 1997 | 44.2999992371 | | 1996 | 25.7999992371 | | 1995 | 24.6000003815 | | 1994 | 21 | | 1993 | 21 | | 1992 | 19.2000007629 | | 1991 | 9.1999998093 | | 1990 | 9 | | 1989 | 23.3999996185 | | 1988 | 11.8999996185 | | 1987 | 11.3999996185 | | 1986 | 7.1999998093 | | 1985 | 9 | | 1984 | 8.1000003815 | | 1983 | 6.3000001907 | | 1982 | 5.1999998093 | | 1981 | 4.9000000954 | | 1980 | 6.4000000954 | | 1979 | 7.5 | | 1978 | 7.0999999046 | | 1977 | 6.6999998093 | | 1976 | 7.0999999046 | | 1975 | 4.6999998093 | | 1974 | 4.8000001907 | | 1973 | 3.7000000477 | | 1972 | 3.7999999523 | | 1971 | 5.3000001907 | | 1970 | 6.3000001907 |
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