| Year | Value | | 2022 | 50.613754211457 | | 2021 | 50.637859273526 | | 2020 | 50.660175372105 | | 2019 | 50.68428288463 | | 2018 | 50.710951684585 | | 2017 | 50.73873858538 | | 2016 | 50.767925902346 | | 2015 | 50.797604586904 | | 2014 | 50.82902686787 | | 2013 | 50.861638883866 | | 2012 | 50.894678278253 | | 2011 | 50.927864652766 | | 2010 | 50.959597248631 | | 2009 | 50.990770012493 | | 2008 | 51.023661829134 | | 2007 | 51.058754753297 | | 2006 | 51.093812208691 | | 2005 | 51.126284959263 | | 2004 | 51.157564648789 | | 2003 | 51.187357152684 | | 2002 | 51.213989817046 | | 2001 | 51.236857592772 | | 2000 | 51.257221641322 | | 1999 | 51.262687799323 | | 1998 | 51.247011370095 | | 1997 | 51.244835230631 | | 1996 | 51.263716416916 | | 1995 | 51.28130308927 | | 1994 | 51.296648271824 | | 1993 | 51.310371976256 | | 1992 | 51.320358508716 | | 1991 | 51.325242288621 | | 1990 | 51.326330104946 | | 1989 | 51.326130537371 | | 1988 | 51.325020146753 | | 1987 | 51.321294086221 | | 1986 | 51.313391429153 | | 1985 | 51.302872608012 | | 1984 | 51.290213380576 | | 1983 | 51.27476805205 | | 1982 | 51.256187181906 | | 1981 | 51.233139674563 | | 1980 | 51.20606834708 | | 1979 | 51.250124756876 | | 1978 | 51.292413209657 | | 1977 | 51.254373228608 | | 1976 | 51.210100768028 | | 1975 | 51.159201679717 | | 1974 | 51.096097348198 | | 1973 | 51.015661394257 | | 1972 | 50.926252202366 | | 1971 | 50.82396833647 | | 1970 | 50.719919954434 | | 1969 | 50.614581207049 | | 1968 | 50.506362740477 | | 1967 | 50.399037287663 | | 1966 | 50.279903572211 | | 1965 | 50.148709053075 | | 1964 | 50.009399116991 | | 1963 | 49.867237773623 | | 1962 | 49.771087010649 | | 1961 | 49.72294964732 | | 1960 | 49.744520558611 |
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