| Year | Value | | 2009 | 7.581 | | 2008 | 8.34 | | 2007 | 8.632 | | 2006 | 9.591 | | 2005 | 8.06 | | 2004 | 7.533 | | 2003 | 6.666 | | 2002 | 6.06 | | 2001 | 6 | | 2000 | 9 | | 1998 | 0.400000006 | | 1996 | 0.3000000119 | | 1995 | 0.200000003 | | 1994 | 0.200000003 | | 1993 | 0.1000000015 | | 1992 | 0.1000000015 | | 1990 | 2.2000000477 | | 1989 | 2 | | 1988 | 2 | | 1987 | 2.5 | | 1986 | 1.5 | | 1985 | 1.2999999523 | | 1984 | 1.2999999523 | | 1983 | 1.2999999523 | | 1982 | 1.1000000238 | | 1981 | 0.8999999762 | | 1980 | 0.8999999762 | | 1979 | 0.8999999762 | | 1978 | 0.8999999762 | | 1977 | 0.8999999762 | | 1976 | 0.8000000119 | | 1975 | 0.6999999881 |
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