| Year | Value | | 2022 | 50.246157416578 | | 2021 | 50.259023393169 | | 2020 | 50.270571621157 | | 2019 | 50.282974534883 | | 2018 | 50.300337516708 | | 2017 | 50.320135126168 | | 2016 | 50.340884668864 | | 2015 | 50.365069438866 | | 2014 | 50.391431047424 | | 2013 | 50.420849473544 | | 2012 | 50.451622356762 | | 2011 | 50.483432188376 | | 2010 | 50.520086203559 | | 2009 | 50.556114921365 | | 2008 | 50.591966568198 | | 2007 | 50.629135189132 | | 2006 | 50.662773316566 | | 2005 | 50.692436857371 | | 2004 | 50.721332320241 | | 2003 | 50.750355784523 | | 2002 | 50.748477719756 | | 2001 | 50.713339898841 | | 2000 | 50.675216463693 | | 1999 | 50.633620217415 | | 1998 | 50.588597901915 | | 1997 | 50.542899707062 | | 1996 | 50.495985364366 | | 1995 | 50.447005405928 | | 1994 | 50.406092801783 | | 1993 | 50.391719998733 | | 1992 | 50.409527730067 | | 1991 | 50.448992926862 | | 1990 | 50.499031342974 | | 1989 | 50.554148511801 | | 1988 | 50.612122555647 | | 1987 | 50.669434601056 | | 1986 | 50.724763211771 | | 1985 | 50.780879435673 | | 1984 | 50.836568468886 | | 1983 | 50.849649870595 | | 1982 | 50.820542724452 | | 1981 | 50.774992394117 | | 1980 | 50.727957405237 | | 1979 | 50.698045759579 | | 1978 | 50.66882227248 | | 1977 | 50.643623434274 | | 1976 | 50.620515466202 | | 1975 | 50.597233847113 | | 1974 | 50.575555047537 | | 1973 | 50.568323497631 | | 1972 | 50.575592316873 | | 1971 | 50.583391663314 | | 1970 | 50.593780202031 | | 1969 | 50.605428218795 | | 1968 | 50.615945876098 | | 1967 | 50.626839705482 | | 1966 | 50.639211621336 | | 1965 | 50.649585537842 | | 1964 | 50.658751050126 | | 1963 | 50.669433612869 | | 1962 | 50.681963486538 | | 1961 | 50.694861989138 | | 1960 | 50.707245608021 |
|