| Year | Value | | 2021 | 4.359006 | | 2020 | 0.857297 | | 2019 | 0.962933 | | 2018 | 0.487269 | | 2017 | 0.281228 | | 2016 | 0.536721 | | 2015 | 2.213882 | | 2014 | 0.564368726 | | 2013 | 0.003641454 | | 2012 | 1.6279873074111 | | 2011 | 1.1747517401172 | | 2010 | 1.249246 | | 2009 | 0.781 | | 2008 | 1.446 | | 2007 | 1.447 | | 2006 | 1.69 | | 2005 | 1.853 | | 2004 | 2.25 | | 2003 | 1.785 | | 2002 | 2.321 | | 2001 | 3.252 | | 2000 | 3.449 | | 1999 | 2.2999999523 | | 1998 | 3.5 | | 1997 | 3.0999999046 | | 1996 | 3 | | 1995 | 2.9000000954 | | 1994 | 2.0999999046 | | 1993 | 1.7999999523 | | 1992 | 2.0999999046 | | 1991 | 4.1999998093 | | 1990 | 1.3999999762 | | 1989 | 1.6000000238 | | 1988 | 2.7000000477 | | 1987 | 2.5 | | 1986 | 2 | | 1985 | 3.2999999523 | | 1984 | 2.4000000954 | | 1983 | 1.3999999762 | | 1982 | 1.2000000477 | | 1981 | 1.2000000477 | | 1980 | 1.8999999762 | | 1979 | 1.2999999523 | | 1978 | 0.8000000119 | | 1977 | 0.3000000119 | | 1976 | 3.2000000477 | | 1975 | 2.7999999523 | | 1974 | 2.9000000954 | | 1973 | 2.5999999046 | | 1972 | 6.6999998093 | | 1971 | 9.1999998093 | | 1970 | 9.3999996185 |
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