| Year | Value | | 2023 | 87.3 | | 2022 | 85.3 | | 2021 | 86.4 | | 2020 | 83.4 | | 2019 | 85.8 | | 2018 | 85.5 | | 2017 | 86 | | 2016 | 84 | | 2015 | 84.5 | | 2014 | 83.2 | | 2013 | 83.9 | | 2012 | 85.2 | | 2011 | 84.2 | | 2010 | 84.3 | | 2009 | 83.6 | | 2008 | 85.5 | | 2007 | 83.6 | | 2006 | 83.1 | | 2005 | 84.1 | | 2004 | 85.1 | | 2003 | 81.6 | | 2002 | 82.3 | | 2001 | 82.4 | | 2000 | 79.9 | | 1999 | 82.9 | | 1998 | 82.1 | | 1997 | 80.4 | | 1996 | 81.6 | | 1995 | 79.9 | | 1994 | 81.7 | | 1993 | 81.58 | | 1992 | 81.754 | | 1991 | 81.819 | | 1990 | 81.837 | | 1989 | 81.781 | | 1988 | 81.615 | | 1987 | 81.468 | | 1986 | 81.028 | | 1985 | 80.595 | | 1984 | 79.888 | | 1983 | 79.244 | | 1982 | 78.35 | | 1981 | 77.972 | | 1980 | 77.489 | | 1979 | 77.404 | | 1978 | 77.381 | | 1977 | 77.585 | | 1976 | 77.648 | | 1975 | 77.763 |
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