| Year | Value | | 2022 | 50.486969976883 | | 2021 | 50.494191207544 | | 2020 | 50.500936673696 | | 2019 | 50.505017059988 | | 2018 | 50.508309848684 | | 2017 | 50.511603147475 | | 2016 | 50.512596024857 | | 2015 | 50.514039518891 | | 2014 | 50.516356884821 | | 2013 | 50.518662249126 | | 2012 | 50.518916888949 | | 2011 | 50.517246732396 | | 2010 | 50.516315058727 | | 2009 | 50.51453720522 | | 2008 | 50.511888537492 | | 2007 | 50.509413026656 | | 2006 | 50.507580958577 | | 2005 | 50.505809658489 | | 2004 | 50.503242825926 | | 2003 | 50.498668588534 | | 2002 | 50.490719220659 | | 2001 | 50.477035908004 | | 2000 | 50.456357674871 | | 1999 | 50.431093983481 | | 1998 | 50.405231404433 | | 1997 | 50.380069079951 | | 1996 | 50.352500309419 | | 1995 | 50.327010307533 | | 1994 | 50.30974185313 | | 1993 | 50.297196342296 | | 1992 | 50.282152374741 | | 1991 | 50.262785855585 | | 1990 | 50.24450459954 | | 1989 | 50.226085299475 | | 1988 | 50.209121605705 | | 1987 | 50.194676180262 | | 1986 | 50.17760925915 | | 1985 | 50.159465761303 | | 1984 | 50.142943443163 | | 1983 | 50.127111790216 | | 1982 | 50.114827173248 | | 1981 | 50.107555373361 | | 1980 | 50.104040905078 | | 1979 | 50.107403922844 | | 1978 | 50.116924536876 | | 1977 | 50.130750694703 | | 1976 | 50.148465373063 | | 1975 | 50.170644534343 | | 1974 | 50.196589485625 | | 1973 | 50.222988798122 | | 1972 | 50.247512351197 | | 1971 | 50.269467489602 | | 1970 | 50.29029410001 | | 1969 | 50.313110177169 | | 1968 | 50.337911018216 | | 1967 | 50.364481802402 | | 1966 | 50.392589638086 | | 1965 | 50.424054839513 | | 1964 | 50.456778187407 | | 1963 | 50.489420805671 | | 1962 | 50.526174987648 | | 1961 | 50.565721451439 | | 1960 | 50.606962081188 |
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