Year | Value | 2023 | 6.678 | 2022 | 8.281 | 2021 | 10.293 | 2020 | 18.548 | 2019 | 6.409 | 2018 | 5.313 | 2017 | 5.461 | 2016 | 4.843 | 2015 | 4.402 | 2014 | 4.444 | 2013 | 3.732 | 2012 | 3.714 | 2011 | 3.922 | 2010 | 5.832 | 2009 | 6.56 | 2008 | 4.868 | 2007 | 6.78 | 2006 | 9.11 | 2005 | 10.33 | 2004 | 12.44 | 2003 | 13.62 | 2002 | 14.11 | 2001 | 14.71 | 2000 | 13.53 | 1999 | 11.75 | 1998 | 14.02 | 1997 | 13.37 | 1996 | 14.32 | 1995 | 14.01 | 1994 | 14 | 1993 | 13.26 | 1992 | 14.67 | 1991 | 16.12 | 1990 | 11.6 | 1989 | 16.31 | 1988 | 16.33 | 1987 | 11.84 | 1986 | 10.53 | 1985 | 12.34 | 1984 | 10.08 | 1983 | 9.71 | 1982 | 8.41 | 1979 | 8.78 | 1978 | 8.06 | 1977 | 8.73 | 1976 | 6.67 | 1975 | 6.41 | 1974 | 5.8 | 1973 | 6.99 | 1972 | 6.79 | 1971 | 7.6 | 1970 | 7.1 |
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