| Year | Value | | 2023 | 72.243 | | 2022 | 70.918 | | 2021 | 66.232 | | 2020 | 66.89 | | 2019 | 71.587 | | 2018 | 71.422 | | 2017 | 71.5 | | 2016 | 71.738 | | 2015 | 71.883 | | 2014 | 71.877 | | 2013 | 71.721 | | 2012 | 71.5 | | 2011 | 71.292 | | 2010 | 71.121 | | 2009 | 71.099 | | 2008 | 71.249 | | 2007 | 71.425 | | 2006 | 71.442 | | 2005 | 71.35 | | 2004 | 71.174 | | 2003 | 71.042 | | 2002 | 70.805 | | 2001 | 70.562 | | 2000 | 70.139 | | 1999 | 69.695 | | 1998 | 69.231 | | 1997 | 68.87 | | 1996 | 68.449 | | 1995 | 67.967 | | 1994 | 67.492 | | 1993 | 67.072 | | 1992 | 66.749 | | 1991 | 66.437 | | 1990 | 66.122 | | 1989 | 65.688 | | 1988 | 65.36 | | 1987 | 64.942 | | 1986 | 64.415 | | 1985 | 63.767 | | 1984 | 63.166 | | 1983 | 62.623 | | 1982 | 62.052 | | 1981 | 61.487 | | 1980 | 61.11 | | 1979 | 60.811 | | 1978 | 60.531 | | 1977 | 60.236 | | 1976 | 59.868 |
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