| Year | Value | | 2022 | 50.430525749004 | | 2021 | 50.438688062737 | | 2020 | 50.448782910862 | | 2019 | 50.560310737938 | | 2018 | 50.737435326378 | | 2017 | 50.834026511867 | | 2016 | 50.891297730267 | | 2015 | 50.95353756271 | | 2014 | 51.018797371403 | | 2013 | 51.078091170626 | | 2012 | 51.105847151793 | | 2011 | 51.103116471506 | | 2010 | 51.093472251813 | | 2009 | 51.087014622279 | | 2008 | 51.084035426182 | | 2007 | 51.072321789395 | | 2006 | 51.046584455708 | | 2005 | 51.011873118851 | | 2004 | 50.976709268784 | | 2003 | 50.956668269509 | | 2002 | 50.954418090131 | | 2001 | 50.945924995996 | | 2000 | 50.908341992485 | | 1999 | 50.850764341877 | | 1998 | 50.785738957345 | | 1997 | 50.722512428983 | | 1996 | 50.692364160295 | | 1995 | 50.706131071319 | | 1994 | 50.73161570774 | | 1993 | 50.751229383654 | | 1992 | 50.774098013255 | | 1991 | 50.784510220735 | | 1990 | 50.759097648223 | | 1989 | 50.700096437801 | | 1988 | 50.619330145157 | | 1987 | 50.544787767658 | | 1986 | 50.492355876016 | | 1985 | 50.451909155551 | | 1984 | 50.409495621996 | | 1983 | 50.370905020673 | | 1982 | 50.340597936856 | | 1981 | 50.305224731081 | | 1980 | 50.273420421153 | | 1979 | 50.235367007378 | | 1978 | 50.185919256832 | | 1977 | 50.143385880566 | | 1976 | 50.111899308526 | | 1975 | 50.092749694065 | | 1974 | 50.079597425013 | | 1973 | 50.068676571929 | | 1972 | 50.064672334825 | | 1971 | 50.058541907396 | | 1970 | 50.061170774994 | | 1969 | 50.059217213044 | | 1968 | 50.001578134529 | | 1967 | 49.911125723709 | | 1966 | 49.857284205225 | | 1965 | 49.844635744922 | | 1964 | 49.831547937041 | | 1963 | 49.797561127327 | | 1962 | 49.759583575828 | | 1961 | 49.750556933925 | | 1960 | 49.751783667739 |
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