| Year | Value | | 2023 | 83.89 | | 2022 | 83.54 | | 2021 | 83.96 | | 2020 | 83.84 | | 2019 | 84.32 | | 2018 | 83.96 | | 2017 | 84 | | 2016 | 84.04 | | 2015 | 83.89 | | 2014 | 83.91 | | 2013 | 83.85 | | 2012 | 83.82 | | 2011 | 83.68 | | 2010 | 83.54 | | 2009 | 83.33 | | 2008 | 83.05 | | 2007 | 82.91 | | 2006 | 82.91 | | 2005 | 82.52 | | 2004 | 82.42 | | 2003 | 82.23 | | 2002 | 82.02 | | 2001 | 82 | | 2000 | 81.82 | | 1999 | 81.61 | | 1998 | 81.41 | | 1997 | 81.25 | | 1996 | 81.15 | | 1995 | 81.03 | | 1994 | 80.95 | | 1993 | 80.86 | | 1992 | 81.07 | | 1991 | 80.81 | | 1990 | 80.73 | | 1989 | 80.49 | | 1988 | 80.27 | | 1987 | 80.19 | | 1986 | 79.87 | | 1985 | 79.8 | | 1984 | 79.82 | | 1983 | 79.61 | | 1982 | 79.29 | | 1981 | 79.16 | | 1980 | 78.79 | | 1979 | 78.59 | | 1978 | 78.32 | | 1977 | 77.97 | | 1976 | 77.59 |
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