| Year | Value | | 2021 | 84.9 | | 2020 | 84.5 | | 2019 | 85.2 | | 2018 | 84.6 | | 2017 | 84.4 | | 2016 | 85.4 | | 2015 | 84.7 | | 2014 | 85.2 | | 2013 | 83.9 | | 2012 | 83.8 | | 2011 | 83.6 | | 2010 | 83.5 | | 2009 | 83.3 | | 2008 | 83.1 | | 2007 | 82.2 | | 2006 | 81.9 | | 2005 | 82.3 | | 2004 | 82.4 | | 2003 | 80.8 | | 2002 | 81.5 | | 2001 | 81 | | 2000 | 81.1 | | 1999 | 81.1 | | 1998 | 80.5 | | 1997 | 79.8 | | 1996 | 79.9 | | 1995 | 80.2 | | 1994 | 79.7 | | 1993 | 79.4 | | 1992 | 79.1 | | 1991 | 79.1 | | 1990 | 78.617 | | 1989 | 77.894 | | 1988 | 78.664 | | 1987 | 77.432 | | 1986 | 77.817 | | 1985 | 77.159 | | 1984 | 76.656 | | 1983 | 76.43 | | 1982 | 76.395 | | 1981 | 75.971 | | 1980 | 75.407 | | 1979 | 76.141 | | 1978 | 75.305 | | 1977 | 75.358 | | 1976 | 73.707 | | 1975 | 73.843 | | 1974 | 73.846 | | 1973 | 74.362 | | 1972 | 73.93 | | 1971 | 72.881 | | 1970 | 73.259 | | 1969 | 73.042 | | 1968 | 72.773 | | 1967 | 72.782 | | 1966 | 72.614 | | 1965 | 72.536 | | 1964 | 73.08 | | 1963 | 71.749 | | 1962 | 71.5 | | 1961 | 72.214 | | 1960 | 71.51 |
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