| Year | Value | | 2021 | 67.344968325011 | | 2020 | 68.383197449278 | | 2019 | 69.156070804147 | | 2018 | 68.958745309586 | | 2017 | 68.651794255574 | | 2016 | 68.448703682455 | | 2015 | 68.178696578776 | | 2014 | 67.869653632974 | | 2013 | 67.511143446837 | | 2012 | 67.197956802001 | | 2011 | 66.899283715838 | | 2010 | 66.545950119502 | | 2009 | 66.24776573128 | | 2008 | 65.850870055858 | | 2007 | 65.653435987572 | | 2006 | 65.40137881884 | | 2005 | 65.032625769415 | | 2004 | 64.671851689103 | | 2003 | 64.442765050683 | | 2002 | 64.144692543589 | | 2001 | 63.827778525296 | | 2000 | 63.520192203477 | | 1999 | 63.209422498435 | | 1998 | 62.820995315757 | | 1997 | 62.543081910681 | | 1996 | 62.180839085467 | | 1995 | 61.872844634624 | | 1994 | 61.631122794036 | | 1993 | 61.336525495036 | | 1992 | 61.149870053301 | | 1991 | 60.879995506601 | | 1990 | 60.643991606821 | | 1989 | 60.458786243338 | | 1988 | 60.046530396823 | | 1987 | 59.85794963162 | | 1986 | 59.527897356824 | | 1985 | 59.062620884444 | | 1984 | 58.668145315639 | | 1983 | 58.324260956317 | | 1982 | 58.01967595709 | | 1981 | 57.643740969482 | | 1980 | 57.288048547395 | | 1979 | 56.889592993796 | | 1978 | 56.453312456903 | | 1977 | 56.055031878694 | | 1976 | 55.570480635995 | | 1975 | 55.031946895524 | | 1974 | 54.508225366923 | | 1973 | 54.076966271177 | | 1972 | 53.441914747519 | | 1971 | 52.219196302839 | | 1970 | 52.274719486552 | | 1969 | 51.901016897118 | | 1968 | 51.475468064029 | | 1967 | 50.800981962072 | | 1966 | 50.314544517629 | | 1965 | 49.583093163083 | | 1964 | 49.922139415234 | | 1963 | 49.385885491477 | | 1962 | 48.954742462682 | | 1961 | 45.804805284756 | | 1960 | 43.389164214161 |
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