| Year | Value | | 2024 | 11.729 | | 2023 | 11.495 | | 2022 | 11.502 | | 2021 | 11.538 | | 2020 | 11.13 | | 2019 | 10.631 | | 2018 | 10.341 | | 2017 | 10.047 | | 2016 | 9.774 | | 2015 | 9.503 | | 2014 | 9.241 | | 2013 | 9.053 | | 2012 | 9.143 | | 2011 | 9.195 | | 2010 | 9.261 | | 2009 | 9.349 | | 2008 | 9.485 | | 2007 | 9.629 | | 2006 | 9.798 | | 2005 | 9.915 | | 2004 | 9.857 | | 2003 | 9.884 | | 2002 | 9.943 | | 2001 | 9.961 | | 2000 | 9.922 | | 1999 | 9.8 | | 1998 | 9.77 | | 1997 | 9.787 | | 1996 | 9.842 | | 1995 | 9.944 | | 1994 | 10.039 | | 1993 | 10.108 | | 1992 | 10.119 | | 1991 | 10.158 | | 1990 | 10.157 | | 1989 | 9.845 | | 1988 | 9.548 | | 1987 | 9.305 | | 1986 | 9.132 | | 1985 | 9.097 | | 1984 | 9.122 | | 1983 | 9.186 | | 1982 | 9.246 | | 1981 | 9.326 | | 1980 | 9.445 | | 1979 | 9.54 | | 1978 | 9.642 | | 1977 | 9.831 | | 1976 | 10.067 |
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