| Year | Value | | 2021 | 72.355288032121 | | 2020 | 73.394299825952 | | 2019 | 73.975920625617 | | 2018 | 73.768334856459 | | 2017 | 73.526085353096 | | 2016 | 73.247060600137 | | 2015 | 72.9484411123 | | 2014 | 72.682981539313 | | 2013 | 72.399181650538 | | 2012 | 72.060328370412 | | 2011 | 71.717612480238 | | 2010 | 71.335998813097 | | 2009 | 71.040732929035 | | 2008 | 70.588245972759 | | 2007 | 70.419661901104 | | 2006 | 70.109354905838 | | 2005 | 69.685381790365 | | 2004 | 69.247866245139 | | 2003 | 69.00868824433 | | 2002 | 68.699063529495 | | 2001 | 68.375823863039 | | 2000 | 67.902082203254 | | 1999 | 67.537253071783 | | 1998 | 67.244930183268 | | 1997 | 66.886113984219 | | 1996 | 66.52341155422 | | 1995 | 66.30947389447 | | 1994 | 66.010941903265 | | 1993 | 65.788083764794 | | 1992 | 65.507351533889 | | 1991 | 65.206692376942 | | 1990 | 65.136815051034 | | 1989 | 64.921548150177 | | 1988 | 64.559314565431 | | 1987 | 64.300505761048 | | 1986 | 63.940423672942 | | 1985 | 63.478721796934 | | 1984 | 63.140276210384 | | 1983 | 62.803392125958 | | 1982 | 62.4790648717 | | 1981 | 62.041508123774 | | 1980 | 61.554682901629 | | 1979 | 61.067333148679 | | 1978 | 60.550437919991 | | 1977 | 60.037218590792 | | 1976 | 59.405485279405 | | 1975 | 58.852477743044 | | 1974 | 58.32295327767 | | 1973 | 57.810144184518 | | 1972 | 57.174900265863 | | 1971 | 56.358830780982 | | 1970 | 56.035205335028 | | 1969 | 55.684728483209 | | 1968 | 55.297587516869 | | 1967 | 54.634885012956 | | 1966 | 54.144994127725 | | 1965 | 53.585079249114 | | 1964 | 53.662484287095 | | 1963 | 53.116912275188 | | 1962 | 52.673684020417 | | 1961 | 49.450364499907 | | 1960 | 46.951701782134 |
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