| Year | Value | | 2021 | 75.768534553178 | | 2020 | 75.768534553178 | | 2019 | 75.757414365844 | | 2018 | 75.792016555029 | | 2017 | 75.804775908076 | | 2016 | 75.783510319665 | | 2015 | 75.788269890541 | | 2014 | 75.799161357077 | | 2013 | 75.810052823613 | | 2012 | 75.810052823613 | | 2011 | 75.777378424005 | | 2010 | 75.739258291129 | | 2009 | 75.735133957743 | | 2008 | 75.680679590503 | | 2007 | 75.675234153779 | | 2006 | 75.570440559821 | | 2005 | 75.328212670916 | | 2004 | 75.747671188103 | | 2003 | 75.238302739801 | | 2002 | 74.866688431821 | | 2001 | 74.670802045925 | | 2000 | 74.605506583959 | | 1999 | 74.910218739798 | | 1998 | 74.839481989335 | | 1997 | 75.111546414191 | | 1996 | 75.035368375231 | | 1995 | 75.029927086734 | | 1994 | 75.013603221243 | | 1993 | 74.230057677658 | | 1992 | 74.072260311242 | | 1991 | 73.522690173033 | | 1990 | 73.430188268582 | | 1989 | 73.413864403091 | | 1988 | 74.725214930896 | | 1987 | 75.671999129394 | | 1986 | 75.742735879856 | | 1985 | 75.911415823267 | | 1984 | 76.031124170203 | | 1983 | 76.129067363152 | | 1982 | 76.7929045598 | | 1981 | 76.803787136794 | | 1980 | 76.515398846447 | | 1979 | 75.960387419741 | | 1978 | 76.2270105561 | | 1977 | 76.39569049951 | | 1976 | 77.337033409511 | | 1975 | 76.760256828817 | | 1974 | 78.991185112635 | | 1973 | 78.778974861247 | | 1972 | 77.054086407661 | | 1971 | 73.228860594189 | | 1970 | 73.234301882686 | | 1969 | 73.158123843726 | | 1968 | 73.027532919795 | | 1967 | 74.164762215693 | | 1966 | 74.164762215693 | | 1965 | 77.804984220263 | | 1964 | 80.824899336163 | | 1963 | 81.842420285123 | | 1962 | 81.456088801828 | | 1961 | 81.298291435412 |
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