| Year | Value | | 2022 | 4.291 | | 2021 | 5.097 | | 2020 | 7.179 | | 2019 | 3.379 | | 2018 | 3.492 | | 2017 | 3.691 | | 2016 | 3.741 | | 2015 | 3.272 | | 2014 | 3.208 | | 2013 | 3.575 | | 2012 | 3.238 | | 2011 | 3.477 | | 2010 | 3.596 | | 2009 | 3.964 | | 2008 | 4.025 | | 2007 | 4.079 | | 2006 | 4.172 | | 2005 | 4.866 | | 2004 | 4.707 | | 2003 | 4.151 | | 2002 | 4.84 | | 2001 | 4.848 | | 2000 | 4.069 | | 1999 | 4.367 | | 1998 | 4.972 | | 1997 | 7.69 | | 1996 | 7.07 | | 1993 | 7.11 | | 1992 | 9.4 | | 1991 | 5.8 | | 1990 | 8.6 | | 1989 | 7.92 | | 1987 | 3.63 | | 1986 | 5.32 | | 1985 | 11.79 | | 1984 | 10.5 | | 1983 | 9.2 | | 1982 | 6.98 | | 1981 | 6.77 | | 1980 | 6.97 | | 1979 | 7.12 | | 1978 | 6.5 | | 1977 | 5.82 | | 1976 | 5.2 | | 1975 | 4.92 | | 1974 | 4 | | 1973 | 4.23 | | 1972 | 4.4 | | 1971 | 4.57 | | 1970 | 4.84 | | 1969 | 5.9 |
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