| Year | Value | | 2021 | 63.591460243979 | | 2020 | 64.046281026426 | | 2019 | 64.492572567009 | | 2018 | 64.225892861079 | | 2017 | 63.892761436733 | | 2016 | 63.514597661386 | | 2015 | 63.174522614002 | | 2014 | 62.864816492083 | | 2013 | 62.592377401085 | | 2012 | 62.22839328965 | | 2011 | 61.974321117279 | | 2010 | 61.275032962954 | | 2009 | 61.114417427232 | | 2008 | 59.997563546778 | | 2007 | 60.168682128991 | | 2006 | 59.69943276833 | | 2005 | 59.227418624531 | | 2004 | 58.805864045933 | | 2003 | 58.565860227202 | | 2002 | 58.253297882987 | | 2001 | 57.827974900194 | | 2000 | 57.657349973403 | | 1999 | 57.258716073228 | | 1998 | 56.58714725508 | | 1997 | 56.688400825563 | | 1996 | 56.409066379576 | | 1995 | 56.331981551088 | | 1994 | 56.534141427302 | | 1993 | 56.064684014391 | | 1992 | 55.676670747713 | | 1991 | 55.727869820748 | | 1990 | 55.863366117927 | | 1989 | 55.819193355451 | | 1988 | 54.975551651042 | | 1987 | 55.361976652043 | | 1986 | 54.822948603071 | | 1985 | 54.187142173462 | | 1984 | 54.087530999717 | | 1983 | 54.105868655213 | | 1982 | 54.806139870766 | | 1981 | 54.708156192906 | | 1980 | 54.517831417067 | | 1979 | 54.2209201071 | | 1978 | 53.997925106293 | | 1977 | 53.796067022414 | | 1976 | 53.247030729639 | | 1975 | 52.772011079489 | | 1974 | 52.418316584988 | | 1973 | 52.307344763256 | | 1972 | 51.732211380928 | | 1971 | 51.751164618464 | | 1970 | 51.238221524796 | | 1969 | 50.974581924308 | | 1968 | 50.893369471576 | | 1967 | 50.470913713073 | | 1966 | 50.057817743279 | | 1965 | 50.15507720121 | | 1964 | 50.046575983787 | | 1963 | 49.537930062394 | | 1962 | 49.149972231142 | | 1961 | 48.950960924888 | | 1960 | 48.60006585883 |
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