| Year | Value | | 2021 | 0.058087 | | 2020 | 1.022 | | 2019 | 1.257 | | 2018 | 1.375 | | 2017 | 1.71896 | | 2016 | 1.7692476465087 | | 2015 | 1.53095 | | 2014 | 1.722 | | 2013 | 1.731 | | 2012 | 1.93406 | | 2011 | 2.29862 | | 2010 | 2.13518 | | 2009 | 1.73 | | 2008 | 2.278 | | 2007 | 2.952 | | 2006 | 3.38 | | 2005 | 3.105 | | 2004 | 2.558 | | 2003 | 0.628 | | 2002 | 0.031 | | 2001 | 2.405 | | 2000 | 5.955 | | 1999 | 12.3999996185 | | 1998 | 30.3999996185 | | 1997 | 31.6000003815 | | 1996 | 23.8999996185 | | 1995 | 29.8999996185 | | 1994 | 30.8999996185 | | 1993 | 27.1000003815 | | 1992 | 14.3999996185 | | 1991 | 5.9000000954 | | 1990 | 8 | | 1989 | 7.6999998093 | | 1988 | 9 | | 1987 | 9.6000003815 | | 1986 | 8.6999998093 | | 1985 | 8 | | 1984 | 11.6999998093 | | 1983 | 10.5 | | 1982 | 9.5 | | 1981 | 9 | | 1980 | 8.8999996185 | | 1979 | 8.1000003815 | | 1978 | 7.5999999046 | | 1977 | 7.1999998093 | | 1976 | 7 | | 1975 | 6.5 | | 1974 | 6.5 | | 1973 | 6.3000001907 | | 1972 | 5.5999999046 | | 1971 | 5.0999999046 | | 1970 | 4.9000000954 |
|