| Year | Value | | 2023 | 71.798 | | 2022 | 71.577 | | 2021 | 71.348 | | 2020 | 71.926 | | 2019 | 72.041 | | 2018 | 72.192 | | 2017 | 72.37 | | 2016 | 72.497 | | 2015 | 72.604 | | 2014 | 72.666 | | 2013 | 72.618 | | 2012 | 72.586 | | 2011 | 72.417 | | 2010 | 72.18 | | 2009 | 71.891 | | 2008 | 71.512 | | 2007 | 71.153 | | 2006 | 70.826 | | 2005 | 70.535 | | 2004 | 70.297 | | 2003 | 70.09 | | 2002 | 69.861 | | 2001 | 69.659 | | 2000 | 69.42 | | 1999 | 69.171 | | 1998 | 68.921 | | 1997 | 68.787 | | 1996 | 68.692 | | 1995 | 68.71 | | 1994 | 68.812 | | 1993 | 68.966 | | 1992 | 69.148 | | 1991 | 69.331 | | 1990 | 69.474 | | 1989 | 69.567 | | 1988 | 69.623 | | 1987 | 69.637 | | 1986 | 69.556 | | 1985 | 69.419 | | 1984 | 69.227 | | 1983 | 68.999 | | 1982 | 68.702 | | 1981 | 68.399 | | 1980 | 68.092 | | 1979 | 67.683 | | 1978 | 67.295 | | 1977 | 66.81 | | 1976 | 66.312 |
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