| Year | Value | | 2022 | 50.754226368441 | | 2021 | 50.731588547591 | | 2020 | 50.702753173571 | | 2019 | 50.681419026239 | | 2018 | 50.669262723348 | | 2017 | 50.659656227653 | | 2016 | 50.649532410912 | | 2015 | 50.639814148696 | | 2014 | 50.631135054775 | | 2013 | 50.622170756063 | | 2012 | 50.611841354334 | | 2011 | 50.601494781969 | | 2010 | 50.590329308006 | | 2009 | 50.576893636296 | | 2008 | 50.561896326583 | | 2007 | 50.549197642146 | | 2006 | 50.539333691369 | | 2005 | 50.529351109756 | | 2004 | 50.518854092389 | | 2003 | 50.507883584716 | | 2002 | 50.496072737548 | | 2001 | 50.483951122355 | | 2000 | 50.470657663812 | | 1999 | 50.45738357726 | | 1998 | 50.446363335797 | | 1997 | 50.435314514808 | | 1996 | 50.423947828716 | | 1995 | 50.412654946746 | | 1994 | 50.402264112865 | | 1993 | 50.390754564119 | | 1992 | 50.376906287593 | | 1991 | 50.362310136557 | | 1990 | 50.348002414139 | | 1989 | 50.334528996001 | | 1988 | 50.3216772618 | | 1987 | 50.309046745469 | | 1986 | 50.295984392215 | | 1985 | 50.282994274165 | | 1984 | 50.269061044213 | | 1983 | 50.253821531589 | | 1982 | 50.237091643377 | | 1981 | 50.219268145916 | | 1980 | 50.202703641281 | | 1979 | 50.186126236827 | | 1978 | 50.168836629321 | | 1977 | 50.152386592516 | | 1976 | 50.133147957961 | | 1975 | 50.111204569994 | | 1974 | 50.089228357163 | | 1973 | 50.06630646591 | | 1972 | 50.04307665722 | | 1971 | 50.018766663212 | | 1970 | 50.001198614277 | | 1969 | 49.99092949507 | | 1968 | 49.979888877724 | | 1967 | 49.968639410978 | | 1966 | 49.957232321603 | | 1965 | 49.944994043589 | | 1964 | 49.932080219226 | | 1963 | 49.919020394448 | | 1962 | 49.905294921203 | | 1961 | 49.890256272132 | | 1960 | 49.874267816998 |
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