| Year | Value | | 2022 | 50.200624929163 | | 2021 | 50.22210814616 | | 2020 | 50.242531622082 | | 2019 | 50.264829180415 | | 2018 | 50.288614676143 | | 2017 | 50.313209417193 | | 2016 | 50.33993136988 | | 2015 | 50.36642008842 | | 2014 | 50.39407903442 | | 2013 | 50.423202515838 | | 2012 | 50.452243209426 | | 2011 | 50.488741135812 | | 2010 | 50.52863762688 | | 2009 | 50.562141587364 | | 2008 | 50.596939073498 | | 2007 | 50.632525311473 | | 2006 | 50.666421253477 | | 2005 | 50.697605070909 | | 2004 | 50.724960263537 | | 2003 | 50.738289230458 | | 2002 | 50.749085391454 | | 2001 | 50.768367023874 | | 2000 | 50.784118949 | | 1999 | 50.792994193372 | | 1998 | 50.798909073273 | | 1997 | 50.806948348928 | | 1996 | 50.798424295112 | | 1995 | 50.774450598435 | | 1994 | 50.736590190655 | | 1993 | 50.693065500234 | | 1992 | 50.657158196379 | | 1991 | 50.62999036734 | | 1990 | 50.422562746325 | | 1989 | 50.266310416334 | | 1988 | 50.247926025121 | | 1987 | 50.233113546382 | | 1986 | 50.220525096927 | | 1985 | 50.204400185023 | | 1984 | 50.187333788981 | | 1983 | 50.13818356296 | | 1982 | 50.076723894585 | | 1981 | 50.035332137167 | | 1980 | 49.979944818491 | | 1979 | 49.914425831989 | | 1978 | 49.843727774937 | | 1977 | 49.765170590671 | | 1976 | 49.68699119339 | | 1975 | 49.607808417164 | | 1974 | 49.548448824713 | | 1973 | 49.514404841862 | | 1972 | 49.47757779876 | | 1971 | 49.432294170843 | | 1970 | 49.386463035756 | | 1969 | 49.343106953676 | | 1968 | 49.296305812431 | | 1967 | 49.251008095034 | | 1966 | 49.203637010865 | | 1965 | 49.156344795174 | | 1964 | 49.111733058635 | | 1963 | 49.065202598661 | | 1962 | 49.000280549542 | | 1961 | 48.916184909078 | | 1960 | 48.830545651551 |
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