| Year | Value | | 2021 | 1.021922 | | 2019 | 1.149492 | | 2018 | 0.44987 | | 2017 | 0.229947 | | 2016 | 0.399566257 | | 2015 | 0.50237232 | | 2014 | 0.851628 | | 2013 | 1.97274 | | 2012 | 2.0464735544478 | | 2011 | 1.8302184173153 | | 2010 | 2.248762813 | | 1993 | 17.5 | | 1992 | 1.7999999523 | | 1991 | 3.0999999046 | | 1990 | 4.3000001907 | | 1989 | 2.7999999523 | | 1988 | 2.2999999523 | | 1987 | 2.5 | | 1986 | 2.2000000477 | | 1985 | 2 | | 1984 | 2.2000000477 | | 1983 | 1.8999999762 | | 1982 | 2.7000000477 | | 1981 | 3 | | 1980 | 3.7999999523 | | 1979 | 3.2999999523 | | 1978 | 3.4000000954 | | 1977 | 4.1999998093 | | 1976 | 5.0999999046 | | 1975 | 3 | | 1974 | 3 | | 1973 | 3 | | 1972 | 3.2000000477 | | 1971 | 3.7000000477 | | 1970 | 3.5999999046 |
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