| Year | Value | | 2022 | 52.647547564368 | | 2021 | 52.690403959764 | | 2020 | 52.674121103004 | | 2019 | 52.618014237399 | | 2018 | 52.529073432847 | | 2017 | 52.446199330131 | | 2016 | 52.365980817447 | | 2015 | 52.2843611447 | | 2014 | 52.197426556872 | | 2013 | 52.081394627458 | | 2012 | 51.924791992362 | | 2011 | 51.744167457128 | | 2010 | 51.557748704131 | | 2009 | 51.388553224212 | | 2008 | 51.237115702111 | | 2007 | 51.09198981036 | | 2006 | 50.957022952476 | | 2005 | 50.827288287554 | | 2004 | 50.695862598123 | | 2003 | 50.552684467413 | | 2002 | 50.449455921779 | | 2001 | 50.377790357117 | | 2000 | 50.279790157382 | | 1999 | 50.178224855073 | | 1998 | 50.103007828595 | | 1997 | 49.913107106924 | | 1996 | 49.818663136995 | | 1995 | 49.96721750184 | | 1994 | 50.090729355686 | | 1993 | 50.127327491785 | | 1992 | 50.102876396426 | | 1991 | 50.062714273769 | | 1990 | 50.004925623091 | | 1989 | 49.946689791451 | | 1988 | 49.867069052238 | | 1987 | 49.846872868195 | | 1986 | 49.909989023052 | | 1985 | 49.97125292999 | | 1984 | 50.031182252844 | | 1983 | 50.09048893941 | | 1982 | 50.148265221645 | | 1981 | 50.206279387229 | | 1980 | 50.260376780518 | | 1979 | 50.301568154403 | | 1978 | 50.337616055519 | | 1977 | 50.425862014375 | | 1976 | 50.507389717116 | | 1975 | 50.524260374448 | | 1974 | 50.535885006961 | | 1973 | 50.544046333899 | | 1972 | 50.504802636191 | | 1971 | 50.420152978777 | | 1970 | 50.357674837713 | | 1969 | 50.301329616935 | | 1968 | 50.237415071031 | | 1967 | 50.167250559151 | | 1966 | 50.093336579823 | | 1965 | 50.017663071712 | | 1964 | 49.943644599451 | | 1963 | 49.869463058045 | | 1962 | 49.778736462897 | | 1961 | 49.690061533571 | | 1960 | 49.586489679616 |
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