| Year | Value | | 2024 | 4.734 | | 2023 | 4.792 | | 2022 | 5.232 | | 2021 | 5.953 | | 2020 | 5.832 | | 2019 | 5.859 | | 2018 | 6.114 | | 2017 | 5.644 | | 2016 | 5.647 | | 2015 | 5.773 | | 2014 | 5.29 | | 2013 | 5.294 | | 2012 | 5.425 | | 2011 | 5.474 | | 2010 | 5.586 | | 2009 | 5.748 | | 2008 | 5.892 | | 2007 | 6.08 | | 2006 | 6.292 | | 2005 | 6.503 | | 2004 | 6.755 | | 2003 | 7.004 | | 2002 | 7.302 | | 2001 | 7.597 | | 2000 | 7.905 | | 1999 | 8.201 | | 1998 | 8.505 | | 1997 | 8.821 | | 1996 | 9.181 | | 1995 | 9.576 | | 1994 | 10.042 | | 1993 | 10.312 | | 1992 | 10.648 | | 1991 | 11.01 | | 1990 | 11.304 | | 1989 | 11.706 | | 1988 | 12.175 | | 1987 | 12.655 | | 1986 | 14.067 | | 1985 | 13.792 | | 1984 | 14.452 | | 1983 | 15.2 | | 1982 | 16.145 | | 1981 | 16.753 | | 1980 | 17.599 | | 1979 | 18.431 | | 1978 | 19.243 | | 1977 | 20.144 | | 1976 | 21.035 |
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