| Year | Value | | 2022 | 50.268510324345 | | 2021 | 50.257949146225 | | 2020 | 50.197224175391 | | 2019 | 50.076742828935 | | 2018 | 49.958925393319 | | 2017 | 49.84197423551 | | 2016 | 49.724930861906 | | 2015 | 49.606220883461 | | 2014 | 49.531860792504 | | 2013 | 49.507907356491 | | 2012 | 49.483993555477 | | 2011 | 49.458109189606 | | 2010 | 49.400594083373 | | 2009 | 49.305966333232 | | 2008 | 49.214147459751 | | 2007 | 49.13032583064 | | 2006 | 49.048356898444 | | 2005 | 48.963027327714 | | 2004 | 48.880665410608 | | 2003 | 48.805349925179 | | 2002 | 48.734957280769 | | 2001 | 48.685716476325 | | 2000 | 48.650104644418 | | 1999 | 48.609422427365 | | 1998 | 48.564612913982 | | 1997 | 48.518866957345 | | 1996 | 48.47415464264 | | 1995 | 48.427708017554 | | 1994 | 48.379496537446 | | 1993 | 48.332040458205 | | 1992 | 48.284672632499 | | 1991 | 48.241202494526 | | 1990 | 48.227664922478 | | 1989 | 48.23854397075 | | 1988 | 48.248335186223 | | 1987 | 48.257992011167 | | 1986 | 48.265418080682 | | 1985 | 48.271667661963 | | 1984 | 48.27999615452 | | 1983 | 48.290758886123 | | 1982 | 48.298508887132 | | 1981 | 48.298874926943 | | 1980 | 48.290044542142 | | 1979 | 48.273448671996 | | 1978 | 48.255228317337 | | 1977 | 48.236757100881 | | 1976 | 48.219485444301 | | 1975 | 48.20433627364 | | 1974 | 48.187258672252 | | 1973 | 48.170311591499 | | 1972 | 48.156165787709 | | 1971 | 48.139731411987 | | 1970 | 48.10301122274 | | 1969 | 48.046976941465 | | 1968 | 47.985077499711 | | 1967 | 47.920662187761 | | 1966 | 47.855601497176 | | 1965 | 47.790084536672 | | 1964 | 47.72337981774 | | 1963 | 47.650108673067 | | 1962 | 47.572422980686 | | 1961 | 47.499417460325 | | 1960 | 47.445908934333 |
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