| Year | Value | | 2021 | 2.75098 | | 2020 | 2.903530909 | | 2019 | 6.727273 | | 2018 | 5.14323 | | 2017 | 2.63621 | | 2016 | 2.442 | | 2015 | 3.352 | | 2014 | 3.422 | | 2013 | 3.541 | | 2012 | 5.266 | | 2011 | 6.352 | | 2010 | 6.733 | | 2009 | 6.672 | | 2008 | 11.763 | | 2007 | 11.894 | | 2006 | 11.661 | | 2005 | 11.106 | | 2004 | 11.62 | | 2003 | 11.979 | | 2002 | 12.014 | | 2001 | 13.781 | | 2000 | 14.286 | | 1999 | 10.5 | | 1998 | 11.1999998093 | | 1997 | 9 | | 1996 | 9.6999998093 | | 1995 | 13.6999998093 | | 1994 | 11.8000001907 | | 1993 | 7.3000001907 | | 1992 | 6.4000000954 | | 1991 | 5.5999999046 | | 1990 | 4.8000001907 | | 1989 | 5.5 | | 1988 | 4.9000000954 | | 1987 | 4.6999998093 | | 1986 | 4 | | 1985 | 4.4000000954 | | 1984 | 3.5 | | 1983 | 3.2999999523 | | 1982 | 3.2000000477 | | 1981 | 4.1999998093 | | 1980 | 4.0999999046 | | 1979 | 5 | | 1978 | 3.7999999523 | | 1977 | 4 | | 1976 | 3.5 | | 1975 | 2.5 | | 1974 | 2.5999999046 | | 1973 | 2.2999999523 | | 1972 | 1.7000000477 | | 1971 | 1.8999999762 | | 1970 | 2.4000000954 |
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