| Year | Value | | 2022 | 50.170466562763 | | 2021 | 50.176956196914 | | 2020 | 50.184072594054 | | 2019 | 50.192951649951 | | 2018 | 50.202636365749 | | 2017 | 50.213958451051 | | 2016 | 50.22123002851 | | 2015 | 50.234234860217 | | 2014 | 50.254873214513 | | 2013 | 50.270000878674 | | 2012 | 50.284022963891 | | 2011 | 50.297849726789 | | 2010 | 50.312477482375 | | 2009 | 50.326892278551 | | 2008 | 50.341618992073 | | 2007 | 50.3589991435 | | 2006 | 50.377994952185 | | 2005 | 50.396153821558 | | 2004 | 50.41379530656 | | 2003 | 50.432927127977 | | 2002 | 50.451857190746 | | 2001 | 50.467843419902 | | 2000 | 50.482483552366 | | 1999 | 50.493966676317 | | 1998 | 50.499945664562 | | 1997 | 50.506708732216 | | 1996 | 50.498842777132 | | 1995 | 50.475448222744 | | 1994 | 50.455122783644 | | 1993 | 50.434433898615 | | 1992 | 50.409626878711 | | 1991 | 50.400284550989 | | 1990 | 50.407672748098 | | 1989 | 50.415554986332 | | 1988 | 50.418452220418 | | 1987 | 50.420425851621 | | 1986 | 50.430065071758 | | 1985 | 50.399265811925 | | 1984 | 50.332613967851 | | 1983 | 50.272596993806 | | 1982 | 50.222979767877 | | 1981 | 50.188639754113 | | 1980 | 50.19757789024 | | 1979 | 50.22664288221 | | 1978 | 50.229924952287 | | 1977 | 50.234207900611 | | 1976 | 50.244069229461 | | 1975 | 50.257446016692 | | 1974 | 50.276811793806 | | 1973 | 50.296738309279 | | 1972 | 50.313261917897 | | 1971 | 50.328102957233 | | 1970 | 50.334271010257 | | 1969 | 50.3313918371 | | 1968 | 50.329058716321 | | 1967 | 50.325733296156 | | 1966 | 50.322998537292 | | 1965 | 50.321055256614 | | 1964 | 50.318021029857 | | 1963 | 50.314556657986 | | 1962 | 50.311538036747 | | 1961 | 50.306121186054 | | 1960 | 50.299030303869 |
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