| Year | Value | | 2021 | 66.622495511461 | | 2020 | 66.959647261724 | | 2019 | 67.495454089986 | | 2018 | 67.069757902653 | | 2017 | 66.63073546881 | | 2016 | 66.244510981794 | | 2015 | 65.671115771625 | | 2014 | 65.265496551645 | | 2013 | 64.905441244788 | | 2012 | 64.248272394358 | | 2011 | 63.521125808685 | | 2010 | 62.720209938098 | | 2009 | 62.210977173366 | | 2008 | 61.093796884521 | | 2007 | 60.994146740245 | | 2006 | 60.5195162697 | | 2005 | 59.920269457829 | | 2004 | 59.299302156155 | | 2003 | 58.834246979944 | | 2002 | 58.189512645415 | | 2001 | 57.629073471782 | | 2000 | 57.102662810392 | | 1999 | 56.663113155271 | | 1998 | 55.527172912238 | | 1997 | 55.007485620096 | | 1996 | 54.174666856721 | | 1995 | 54.084258674843 | | 1994 | 53.558961384188 | | 1993 | 52.983172635438 | | 1992 | 52.430377059068 | | 1991 | 51.675875961471 | | 1990 | 52.024943967455 | | 1989 | 51.763001579028 | | 1988 | 50.978350617203 | | 1987 | 51.175758461102 | | 1986 | 50.536455761483 | | 1985 | 49.881789888776 | | 1984 | 49.511848965585 | | 1983 | 49.265175019222 | | 1982 | 49.997956367409 | | 1981 | 49.640681793581 | | 1980 | 49.319924498222 | | 1979 | 48.862592109978 | | 1978 | 48.372491016082 | | 1977 | 47.92173340615 | | 1976 | 47.100775075202 | | 1975 | 46.547126346815 | | 1974 | 46.723799199011 | | 1973 | 46.821552898607 | | 1972 | 46.285417907311 | | 1971 | 42.972650258686 | | 1970 | 44.352360198146 | | 1969 | 45.67813816669 | | 1968 | 45.428891747961 | | 1967 | 45.062329392924 | | 1966 | 44.418321232758 | | 1965 | 44.061920379451 | | 1964 | 44.101614519465 | | 1963 | 43.350270450751 | | 1962 | 43.212490902775 | | 1961 | 42.748886293459 | | 1960 | 42.264526215719 |
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