| Year | Value | | 2022 | 50.081834251548 | | 2021 | 50.081069604781 | | 2020 | 50.082445240126 | | 2019 | 50.086034729771 | | 2018 | 50.089279364452 | | 2017 | 50.093461183574 | | 2016 | 50.100266194567 | | 2015 | 50.108026990216 | | 2014 | 50.11574834286 | | 2013 | 50.123614806395 | | 2012 | 50.132951390499 | | 2011 | 50.144915190926 | | 2010 | 50.157880354201 | | 2009 | 50.170323787212 | | 2008 | 50.182912848007 | | 2007 | 50.196314254377 | | 2006 | 50.211042610911 | | 2005 | 50.22697180063 | | 2004 | 50.243724662174 | | 2003 | 50.261755971738 | | 2002 | 50.279803268358 | | 2001 | 50.295864373303 | | 2000 | 50.30950004689 | | 1999 | 50.316636298826 | | 1998 | 50.316964758724 | | 1997 | 50.321690321985 | | 1996 | 50.329904041852 | | 1995 | 50.337729338255 | | 1994 | 50.341223236288 | | 1993 | 50.342749085817 | | 1992 | 50.352473953465 | | 1991 | 50.371180152228 | | 1990 | 50.388404351719 | | 1989 | 50.401539534867 | | 1988 | 50.411566133714 | | 1987 | 50.417513817487 | | 1986 | 50.42737360009 | | 1985 | 50.437670252707 | | 1984 | 50.444763602463 | | 1983 | 50.447745037265 | | 1982 | 50.452832980358 | | 1981 | 50.461847460544 | | 1980 | 50.472876270509 | | 1979 | 50.487026372463 | | 1978 | 50.50155677211 | | 1977 | 50.516872056218 | | 1976 | 50.533027975351 | | 1975 | 50.549627296559 | | 1974 | 50.567046021621 | | 1973 | 50.580533281077 | | 1972 | 50.587253805018 | | 1971 | 50.594044960179 | | 1970 | 50.603294698465 | | 1969 | 50.612559238668 | | 1968 | 50.622053127684 | | 1967 | 50.631401875882 | | 1966 | 50.639825232003 | | 1965 | 50.647565917914 | | 1964 | 50.656028070041 | | 1963 | 50.664359531107 | | 1962 | 50.673409421562 | | 1961 | 50.684480874909 | | 1960 | 50.693700017797 |
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