| Year | Value | | 2022 | 50.173432295925 | | 2021 | 50.199372027711 | | 2020 | 50.221153867945 | | 2019 | 50.236155261863 | | 2018 | 50.249281116839 | | 2017 | 50.261635609632 | | 2016 | 50.274334708611 | | 2015 | 50.286891282707 | | 2014 | 50.298790570115 | | 2013 | 50.31024108623 | | 2012 | 50.321947717852 | | 2011 | 50.334491855579 | | 2010 | 50.348203285608 | | 2009 | 50.363274549353 | | 2008 | 50.379440893312 | | 2007 | 50.396832282526 | | 2006 | 50.416094892654 | | 2005 | 50.436891236212 | | 2004 | 50.458927493998 | | 2003 | 50.481875136132 | | 2002 | 50.501767517032 | | 2001 | 50.516555467951 | | 2000 | 50.528814542434 | | 1999 | 50.540237415965 | | 1998 | 50.550335750406 | | 1997 | 50.558113056315 | | 1996 | 50.564419508644 | | 1995 | 50.56963450905 | | 1994 | 50.572787005809 | | 1993 | 50.574164162982 | | 1992 | 50.573748126922 | | 1991 | 50.571281738274 | | 1990 | 50.56709519991 | | 1989 | 50.561563723019 | | 1988 | 50.554788646556 | | 1987 | 50.547197817627 | | 1986 | 50.538788628357 | | 1985 | 50.529430365963 | | 1984 | 50.518719028986 | | 1983 | 50.507017667701 | | 1982 | 50.494360142671 | | 1981 | 50.466806963237 | | 1980 | 50.422064677392 | | 1979 | 50.368688560936 | | 1978 | 50.305535893201 | | 1977 | 50.23593918168 | | 1976 | 50.162831916925 | | 1975 | 50.08877710096 | | 1974 | 50.01510527242 | | 1973 | 49.934692392264 | | 1972 | 49.875986909421 | | 1971 | 49.846597317858 | | 1970 | 49.816608940517 | | 1969 | 49.788036458408 | | 1968 | 49.761304529718 | | 1967 | 49.735379624187 | | 1966 | 49.710126118249 | | 1965 | 49.685393436679 | | 1964 | 49.662384496183 | | 1963 | 49.641657554465 | | 1962 | 49.620835880196 | | 1961 | 49.599115602244 | | 1960 | 49.577930251226 |
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