| Year | Value | | 2022 | 48.249209586866 | | 2021 | 48.264550218544 | | 2020 | 48.276926018984 | | 2019 | 48.285651692686 | | 2018 | 48.296489973729 | | 2017 | 48.308123291947 | | 2016 | 48.319712208912 | | 2015 | 48.33031352291 | | 2014 | 48.340237030657 | | 2013 | 48.352967326073 | | 2012 | 48.368973965038 | | 2011 | 48.384403988107 | | 2010 | 48.39694351039 | | 2009 | 48.411228873084 | | 2008 | 48.428982925135 | | 2007 | 48.445084544209 | | 2006 | 48.45662699 | | 2005 | 48.460693934631 | | 2004 | 48.458961145835 | | 2003 | 48.45112703447 | | 2002 | 48.433830635019 | | 2001 | 48.416237431332 | | 2000 | 48.413179627088 | | 1999 | 48.423558309532 | | 1998 | 48.435988762369 | | 1997 | 48.449010832474 | | 1996 | 48.462546346631 | | 1995 | 48.475304758405 | | 1994 | 48.4872459734 | | 1993 | 48.496788388657 | | 1992 | 48.495402914577 | | 1991 | 48.471514541009 | | 1990 | 48.436060776721 | | 1989 | 48.361734998874 | | 1988 | 48.292684542145 | | 1987 | 48.283637798924 | | 1986 | 48.281676505711 | | 1985 | 48.284980211486 | | 1984 | 48.295330957302 | | 1983 | 48.312191155616 | | 1982 | 48.335289203596 | | 1981 | 48.377851192128 | | 1980 | 48.433392008557 | | 1979 | 48.457173776341 | | 1978 | 48.463572545469 | | 1977 | 48.466109280873 | | 1976 | 48.451388272864 | | 1975 | 48.43116138777 | | 1974 | 48.403994395894 | | 1973 | 48.372929188113 | | 1972 | 48.338641785639 | | 1971 | 48.301726523337 | | 1970 | 48.262813350352 | | 1969 | 48.222426287487 | | 1968 | 48.181638259078 | | 1967 | 48.14165523192 | | 1966 | 48.103488644346 | | 1965 | 48.065397249072 | | 1964 | 48.047827752806 | | 1963 | 48.058843594885 | | 1962 | 48.085720616219 | | 1961 | 48.129772007768 | | 1960 | 48.19080926021 |
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