| Year | Value | | 2021 | 73.507333908542 | | 2020 | 73.507333908542 | | 2019 | 73.46419327006 | | 2018 | 73.459879206212 | | 2017 | 73.459879206212 | | 2016 | 73.459879206212 | | 2015 | 73.459879206212 | | 2014 | 73.459879206212 | | 2013 | 73.459879206212 | | 2012 | 73.459879206212 | | 2011 | 73.459879206212 | | 2010 | 73.438308886971 | | 2009 | 73.425366695427 | | 2008 | 73.421052631579 | | 2007 | 73.433994823123 | | 2006 | 73.425366695427 | | 2005 | 73.412424503883 | | 2004 | 73.412424503883 | | 2003 | 73.412424503883 | | 2002 | 73.408110440035 | | 2001 | 72.545297670406 | | 2000 | 69.09404659189 | | 1999 | 66.937014667817 | | 1998 | 64.779982743745 | | 1997 | 64.779982743745 | | 1996 | 63.917169974116 | | 1995 | 62.622950819672 | | 1994 | 60.461604831752 | | 1993 | 60.461604831752 | | 1992 | 59.167385677308 | | 1991 | 57.657463330457 | | 1990 | 56.039689387403 | | 1989 | 56.125970664366 | | 1988 | 56.125970664366 | | 1987 | 56.125970664366 | | 1986 | 56.125970664366 | | 1985 | 56.125970664366 | | 1984 | 56.125970664366 | | 1983 | 56.125970664366 | | 1982 | 56.125970664366 | | 1981 | 56.125970664366 | | 1980 | 56.125970664366 | | 1979 | 56.125970664366 | | 1978 | 56.125970664366 | | 1977 | 56.125970664366 | | 1976 | 56.125970664366 | | 1975 | 56.125970664366 | | 1974 | 56.125970664366 | | 1973 | 56.125970664366 | | 1972 | 56.125970664366 | | 1971 | 56.125970664366 | | 1970 | 56.125970664366 | | 1969 | 56.125970664366 | | 1968 | 56.125970664366 | | 1967 | 56.125970664366 | | 1966 | 56.125970664366 | | 1965 | 56.125970664366 | | 1964 | 56.125970664366 | | 1963 | 56.125970664366 | | 1962 | 56.125970664366 | | 1961 | 56.125970664366 |
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