| Year | Value | | 2021 | 77.658902454567 | | 2020 | 77.735582333602 | | 2019 | 78.665905405038 | | 2018 | 78.351466848203 | | 2017 | 78.263264090061 | | 2016 | 78.190218246258 | | 2015 | 77.827536408216 | | 2014 | 78.049480532526 | | 2013 | 77.627937461031 | | 2012 | 77.269079305374 | | 2011 | 77.167064906335 | | 2010 | 76.667016962594 | | 2009 | 76.373433009614 | | 2008 | 76.12803164452 | | 2007 | 75.838645756206 | | 2006 | 75.559949287791 | | 2005 | 75.162335279302 | | 2004 | 74.980090050622 | | 2003 | 74.46903631639 | | 2002 | 74.341045349822 | | 2001 | 74.201239560426 | | 2000 | 73.806596046818 | | 1999 | 73.423846479898 | | 1998 | 73.157365926219 | | 1997 | 72.847533439633 | | 1996 | 72.475561340524 | | 1995 | 72.159785208705 | | 1994 | 72.011332095627 | | 1993 | 71.75152316615 | | 1992 | 71.581801770563 | | 1991 | 71.278513213122 | | 1990 | 71.20366018053 | | 1989 | 71.193015877608 | | 1988 | 71.110872407882 | | 1987 | 70.909373740615 | | 1986 | 70.690945265669 | | 1985 | 70.409993366764 | | 1984 | 70.325849610396 | | 1983 | 70.064087769717 | | 1982 | 70.036520874542 | | 1981 | 69.75146917234 | | 1980 | 69.411508941173 | | 1979 | 69.418626930855 | | 1978 | 69.167870422497 | | 1977 | 69.101774352204 | | 1976 | 68.845033596977 | | 1975 | 68.610760863946 | | 1974 | 68.657256030591 | | 1973 | 68.370261187759 | | 1972 | 68.277067287119 | | 1971 | 67.89337613595 | | 1970 | 67.821768100394 | | 1969 | 67.437187653083 | | 1968 | 67.687874983831 | | 1967 | 67.724985206673 | | 1966 | 67.776155741595 | | 1965 | 67.511276408788 | | 1964 | 67.415796057148 | | 1963 | 66.948149168155 | | 1962 | 66.63138294608 | | 1961 | 66.843474708568 | | 1960 | 66.491327188388 |
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