| Year | Value | | 2021 | 84.4 | | 2020 | 83 | | 2019 | 84.3 | | 2018 | 83.9 | | 2017 | 83.9 | | 2016 | 84 | | 2015 | 83.4 | | 2014 | 83.9 | | 2013 | 83.2 | | 2012 | 83.1 | | 2011 | 83.3 | | 2010 | 83 | | 2009 | 82.8 | | 2008 | 82.6 | | 2007 | 82.6 | | 2006 | 82.3 | | 2005 | 81.9 | | 2004 | 81.9 | | 2003 | 81.1 | | 2002 | 81.2 | | 2001 | 81.2 | | 2000 | 81 | | 1999 | 81 | | 1998 | 80.7 | | 1997 | 80.7 | | 1996 | 80.66 | | 1995 | 80.38 | | 1994 | 80.19 | | 1993 | 79.9 | | 1992 | 79.87 | | 1991 | 79.67 | | 1990 | 79.54 | | 1989 | 79.09 | | 1988 | 79.1 | | 1987 | 78.9 | | 1986 | 78.23 | | 1985 | 78.08 | | 1984 | 77.98 | | 1983 | 77.27 | | 1982 | 77.33 | | 1981 | 77.12 | | 1980 | 76.69 | | 1979 | 76.61 | | 1978 | 76.14 | | 1977 | 76.18 | | 1976 | 75.49 | | 1975 | 75.28 | | 1974 | 75.31 | | 1973 | 74.98 | | 1972 | 74.76 | | 1971 | 74.4 | | 1970 | 74.25 | | 1969 | 74.13 | | 1968 | 73.92 | | 1967 | 74.25 | | 1966 | 73.8 | | 1965 | 73.76 | | 1964 | 73.9 | | 1963 | 73.14 | | 1962 | 73.18 | | 1961 | 73.63 | | 1960 | 72.77 |
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