| Year | Value | | 2022 | 50.170187741121 | | 2021 | 50.176715161886 | | 2020 | 50.18382815476 | | 2019 | 50.192706886621 | | 2018 | 50.202394398757 | | 2017 | 50.213718715013 | | 2016 | 50.220993717409 | | 2015 | 50.234001604541 | | 2014 | 50.25464485856 | | 2013 | 50.269779429187 | | 2012 | 50.283813186287 | | 2011 | 50.297652167633 | | 2010 | 50.312286654122 | | 2009 | 50.32671741985 | | 2008 | 50.341454235393 | | 2007 | 50.358846704883 | | 2006 | 50.377851520872 | | 2005 | 50.396021651042 | | 2004 | 50.413672586335 | | 2003 | 50.432814866628 | | 2002 | 50.45175070527 | | 2001 | 50.467743781274 | | 2000 | 50.482391414586 | | 1999 | 50.493884014894 | | 1998 | 50.49987105599 | | 1997 | 50.506656630271 | | 1996 | 50.498802685579 | | 1995 | 50.475391659176 | | 1994 | 50.455052054052 | | 1993 | 50.434361519249 | | 1992 | 50.40956032284 | | 1991 | 50.400222914857 | | 1990 | 50.407617237399 | | 1989 | 50.415505126564 | | 1988 | 50.41841225804 | | 1987 | 50.4203873252 | | 1986 | 50.430016723229 | | 1985 | 50.399211942661 | | 1984 | 50.332560000943 | | 1983 | 50.272541719719 | | 1982 | 50.222921784323 | | 1981 | 50.188576573684 | | 1980 | 50.197503126734 | | 1979 | 50.226554977175 | | 1978 | 50.229828759705 | | 1977 | 50.234093419786 | | 1976 | 50.243937998924 | | 1975 | 50.257308125697 | | 1974 | 50.276668007603 | | 1973 | 50.296588413783 | | 1972 | 50.313114044381 | | 1971 | 50.327967368963 | | 1970 | 50.334144481527 | | 1969 | 50.331276075111 | | 1968 | 50.328954819645 | | 1967 | 50.325642713272 | | 1966 | 50.322921956376 | | 1965 | 50.320992914663 | | 1964 | 50.317972456576 | | 1963 | 50.314522767483 | | 1962 | 50.311521420819 | | 1961 | 50.306121887257 | | 1960 | 50.299051246358 |
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