| Year | Value | | 2022 | 48.412082701859 | | 2021 | 48.356678754568 | | 2020 | 48.376261951913 | | 2019 | 48.386847465894 | | 2018 | 48.388831710078 | | 2017 | 48.390299155951 | | 2016 | 48.394776585442 | | 2015 | 48.401142153224 | | 2014 | 48.405844589397 | | 2013 | 48.410368874551 | | 2012 | 48.416802167376 | | 2011 | 48.424883068981 | | 2010 | 48.43206475843 | | 2009 | 48.437665549613 | | 2008 | 48.447932841577 | | 2007 | 48.468750507828 | | 2006 | 48.496550162594 | | 2005 | 48.521166486515 | | 2004 | 48.540433239243 | | 2003 | 48.557720303734 | | 2002 | 48.574323456466 | | 2001 | 48.591203620673 | | 2000 | 48.550116219092 | | 1999 | 48.517756088679 | | 1998 | 48.546899048176 | | 1997 | 48.569811592991 | | 1996 | 48.5897991032 | | 1995 | 48.61035803937 | | 1994 | 48.632494532508 | | 1993 | 48.652631822881 | | 1992 | 48.67507230158 | | 1991 | 48.701454032137 | | 1990 | 48.725579943703 | | 1989 | 48.745458929045 | | 1988 | 48.769459259523 | | 1987 | 48.784759905022 | | 1986 | 48.785200593277 | | 1985 | 48.78081161597 | | 1984 | 48.77063912686 | | 1983 | 48.759123192567 | | 1982 | 48.746946694107 | | 1981 | 48.739650734229 | | 1980 | 48.73583773896 | | 1979 | 48.732340643242 | | 1978 | 48.732789920064 | | 1977 | 48.732210811415 | | 1976 | 48.722968873878 | | 1975 | 48.702740461071 | | 1974 | 48.674687449773 | | 1973 | 48.64930754903 | | 1972 | 48.626215069177 | | 1971 | 48.605008800778 | | 1970 | 48.597348460698 | | 1969 | 48.59581334197 | | 1968 | 48.587772633615 | | 1967 | 48.574885011356 | | 1966 | 48.559287667365 | | 1965 | 48.538014617628 | | 1964 | 48.511910275886 | | 1963 | 48.483926869685 | | 1962 | 48.451969629015 | | 1961 | 48.416443264974 | | 1960 | 48.377664948611 |
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