| Year | Value | | 2021 | 77.268623732827 | | 2020 | 77.437023008886 | | 2019 | 78.465980049997 | | 2018 | 78.251493900643 | | 2017 | 78.164146583479 | | 2016 | 78.084939344259 | | 2015 | 77.937291270499 | | 2014 | 78.018193034077 | | 2013 | 77.752348251901 | | 2012 | 77.532814879676 | | 2011 | 77.360432523738 | | 2010 | 77.070634121703 | | 2009 | 76.855618440993 | | 2008 | 76.535054195495 | | 2007 | 76.332832737693 | | 2006 | 76.074026876783 | | 2005 | 75.739898665123 | | 2004 | 75.600116538155 | | 2003 | 75.168672476851 | | 2002 | 75.018383284354 | | 2001 | 74.828895123526 | | 2000 | 74.496265706707 | | 1999 | 74.122186741627 | | 1998 | 73.928644200256 | | 1997 | 73.695235859867 | | 1996 | 73.324921632171 | | 1995 | 72.890687377755 | | 1994 | 72.797558246098 | | 1993 | 72.530399017663 | | 1992 | 72.420714028788 | | 1991 | 72.150021037914 | | 1990 | 71.960761369555 | | 1989 | 71.864023961932 | | 1988 | 71.654664797591 | | 1987 | 71.536280052848 | | 1986 | 71.263603578049 | | 1985 | 70.988398009499 | | 1984 | 70.864542433939 | | 1983 | 70.591554726882 | | 1982 | 70.485002845898 | | 1981 | 70.150212549597 | | 1980 | 69.765735067077 | | 1979 | 69.694261455815 | | 1978 | 69.381077172221 | | 1977 | 69.252391585714 | | 1976 | 68.896895419363 | | 1975 | 68.632851577131 | | 1974 | 68.366117483998 | | 1973 | 67.975796317139 | | 1972 | 67.803430880737 | | 1971 | 67.586469611533 | | 1970 | 67.310274231148 | | 1969 | 67.003167087627 | | 1968 | 66.865884143781 | | 1967 | 67.118013721965 | | 1966 | 66.879835486671 | | 1965 | 66.669024056531 | | 1964 | 66.565880291127 | | 1963 | 66.142404267047 | | 1962 | 65.98218515735 | | 1961 | 66.073751460408 | | 1960 | 65.689043382314 |
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