| Year | Value | | 2021 | 76.77 | | 2020 | 76.7 | | 2019 | 78.6 | | 2018 | 78.8 | | 2017 | 77.9 | | 2016 | 77.5 | | 2015 | 77.4 | | 2014 | 77.5 | | 2013 | 77.5 | | 2012 | 76.9 | | 2011 | 77.2 | | 2010 | 77.2 | | 2009 | 76.7 | | 2008 | 76.5 | | 2007 | 75.9 | | 2006 | 76.2 | | 2005 | 75.9 | | 2004 | 75.8 | | 2003 | 75.7 | | 2002 | 75.6 | | 2001 | 76.1 | | 2000 | 75.2 | | 1999 | 75.3 | | 1998 | 74.5 | | 1997 | 74.7 | | 1996 | 74.8 | | 1995 | 74 | | 1994 | 74.1 | | 1993 | 74.517 | | 1992 | 73.761 | | 1991 | 74.283 | | 1990 | 73.762 | | 1989 | 73.286 | | 1988 | 72.796 | | 1987 | 72.325 | | 1986 | 72.357 | | 1985 | 72.389 | | 1984 | 72.237 | | 1983 | 71.596 | | 1982 | 71.906 | | 1981 | 71.953 | | 1980 | 71.363 | | 1979 | 71.636 | | 1978 | 71.201 | | 1977 | 70.42 | | 1976 | 69.612 | | 1975 | 68.74 | | 1974 | 68.377 | | 1973 | 67.695 | | 1972 | 67.286 | | 1971 | 66.377 | | 1970 | 65.362 | | 1969 | 64.62 | | 1968 | 64.301 | | 1967 | 63.541 | | 1966 | 63.247 | | 1965 | 61.328 | | 1964 | 60.249 | | 1963 | 57.798 | | 1962 | 58.727 | | 1961 | 58.962 | | 1960 | 57.376 |
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