| Year | Value | | 2021 | 62.277173992767 | | 2020 | 62.828838645804 | | 2019 | 63.137651855593 | | 2018 | 62.728433176881 | | 2017 | 62.305453124715 | | 2016 | 61.886646879535 | | 2015 | 61.367370349726 | | 2014 | 60.9237213867 | | 2013 | 60.395812440899 | | 2012 | 59.780768292617 | | 2011 | 59.13999921811 | | 2010 | 58.353712418177 | | 2009 | 57.69446996429 | | 2008 | 56.836895896882 | | 2007 | 56.212722962814 | | 2006 | 55.531720595476 | | 2005 | 54.786753254529 | | 2004 | 54.166205774941 | | 2003 | 53.70586636054 | | 2002 | 53.276247323389 | | 2001 | 52.934562518143 | | 2000 | 52.752335122316 | | 1999 | 52.442602012049 | | 1998 | 51.812293469938 | | 1997 | 52.031519461079 | | 1996 | 51.922191578109 | | 1995 | 52.013561884897 | | 1994 | 51.878175501447 | | 1993 | 51.777504657066 | | 1992 | 51.525834890591 | | 1991 | 51.717288524659 | | 1990 | 51.935664597757 | | 1989 | 51.911424523097 | | 1988 | 51.176492575854 | | 1987 | 51.452350645215 | | 1986 | 50.969234027512 | | 1985 | 50.56385163121 | | 1984 | 50.30743761883 | | 1983 | 50.176012895682 | | 1982 | 51.020726778436 | | 1981 | 50.754678631041 | | 1980 | 50.357682607944 | | 1979 | 50.002453502694 | | 1978 | 49.574508006913 | | 1977 | 49.174717480921 | | 1976 | 48.646201207573 | | 1975 | 47.86693997969 | | 1974 | 47.481603716627 | | 1973 | 47.276463372533 | | 1972 | 46.641245129123 | | 1971 | 46.524115885525 | | 1970 | 46.015505914264 | | 1969 | 45.66602412238 | | 1968 | 45.422009657109 | | 1967 | 44.997421050913 | | 1966 | 44.578624746593 | | 1965 | 44.666100376707 | | 1964 | 44.517028320782 | | 1963 | 44.03557896543 | | 1962 | 43.710420673017 | | 1961 | 43.39585564249 | | 1960 | 43.015638094803 |
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