| Year | Value | | 2024 | 74.619 | | 2023 | 74.529 | | 2022 | 74.655 | | 2021 | 72.719 | | 2020 | 73.441 | | 2019 | 74.678 | | 2018 | 74.385 | | 2017 | 73.957 | | 2016 | 73.49 | | 2015 | 73.481 | | 2014 | 73.443 | | 2013 | 73.118 | | 2012 | 72.477 | | 2011 | 71.758 | | 2010 | 71.903 | | 2009 | 71.555 | | 2008 | 71.246 | | 2007 | 70.975 | | 2006 | 70.637 | | 2005 | 70.304 | | 2004 | 70.037 | | 2003 | 69.682 | | 2002 | 69.38 | | 2001 | 69.034 | | 2000 | 68.679 | | 1999 | 67.622 | | 1998 | 67.816 | | 1997 | 67.258 | | 1996 | 66.797 | | 1995 | 66.216 | | 1994 | 65.94 | | 1993 | 65.578 | | 1992 | 65.176 | | 1991 | 64.917 | | 1990 | 64.475 | | 1989 | 64.001 | | 1988 | 63.56 | | 1987 | 63.089 | | 1986 | 62.59 | | 1985 | 62.08 | | 1984 | 61.566 | | 1983 | 61.107 | | 1982 | 60.634 | | 1981 | 60.069 | | 1980 | 59.613 | | 1979 | 58.997 | | 1978 | 58.453 | | 1977 | 57.775 | | 1976 | 57.026 |
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