| Year | Value | | 2022 | 50.248603385671 | | 2021 | 50.255609609446 | | 2020 | 50.266743178991 | | 2019 | 50.280095612779 | | 2018 | 50.295143519172 | | 2017 | 50.31114025382 | | 2016 | 50.328736115168 | | 2015 | 50.347353092644 | | 2014 | 50.364055269364 | | 2013 | 50.379858445244 | | 2012 | 50.396119664508 | | 2011 | 50.411064100246 | | 2010 | 50.425385377984 | | 2009 | 50.440535808508 | | 2008 | 50.45505420834 | | 2007 | 50.470388826295 | | 2006 | 50.484603500564 | | 2005 | 50.496798105628 | | 2004 | 50.506981146639 | | 2003 | 50.517043448772 | | 2002 | 50.532870693404 | | 2001 | 50.550911924978 | | 2000 | 50.568291717027 | | 1999 | 50.587647706121 | | 1998 | 50.60496411393 | | 1997 | 50.620534954642 | | 1996 | 50.635891466659 | | 1995 | 50.651007020366 | | 1994 | 50.665829145729 | | 1993 | 50.680497326126 | | 1992 | 50.695328288122 | | 1991 | 50.707022143816 | | 1990 | 50.714153398607 | | 1989 | 50.717617887272 | | 1988 | 50.720771142702 | | 1987 | 50.721584064075 | | 1986 | 50.719024160985 | | 1985 | 50.713728735029 | | 1984 | 50.70421380138 | | 1983 | 50.689885042577 | | 1982 | 50.673221236432 | | 1981 | 50.653298695665 | | 1980 | 50.630371296478 | | 1979 | 50.606514256113 | | 1978 | 50.58340983337 | | 1977 | 50.562330813475 | | 1976 | 50.541617040179 | | 1975 | 50.521341274757 | | 1974 | 50.49913848473 | | 1973 | 50.47611289505 | | 1972 | 50.457411026288 | | 1971 | 50.440958532449 | | 1970 | 50.426846596247 | | 1969 | 50.416234610124 | | 1968 | 50.407376409639 | | 1967 | 50.401097889644 | | 1966 | 50.397704279645 | | 1965 | 50.396555164195 | | 1964 | 50.394466657171 | | 1963 | 50.393585557378 | | 1962 | 50.392531716571 | | 1961 | 50.390490034105 | | 1960 | 50.391173459266 |
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