| Year | Value | | 2022 | 50.778626874517 | | 2021 | 50.770369224788 | | 2020 | 50.759826255903 | | 2019 | 50.743545952066 | | 2018 | 50.725440217486 | | 2017 | 50.704809879239 | | 2016 | 50.680973719771 | | 2015 | 50.653802363969 | | 2014 | 50.628962482887 | | 2013 | 50.606935657552 | | 2012 | 50.583102100912 | | 2011 | 50.558141113146 | | 2010 | 50.543054650046 | | 2009 | 50.558881700165 | | 2008 | 50.594722374529 | | 2007 | 50.616686029738 | | 2006 | 50.615041199083 | | 2005 | 50.60223912823 | | 2004 | 50.589403414716 | | 2003 | 50.57737897246 | | 2002 | 50.563908192711 | | 2001 | 50.547801633751 | | 2000 | 50.532670556126 | | 1999 | 50.524542832421 | | 1998 | 50.519550322224 | | 1997 | 50.511649409355 | | 1996 | 50.501700832373 | | 1995 | 50.488812581021 | | 1994 | 50.471983982683 | | 1993 | 50.45373703298 | | 1992 | 50.436637912169 | | 1991 | 50.420679802495 | | 1990 | 50.406210975382 | | 1989 | 50.39444200952 | | 1988 | 50.383909380506 | | 1987 | 50.373409120498 | | 1986 | 50.363258935091 | | 1985 | 50.351411516974 | | 1984 | 50.337738276133 | | 1983 | 50.323744771727 | | 1982 | 50.310274020122 | | 1981 | 50.296998771924 | | 1980 | 50.295345602786 | | 1979 | 50.334551096071 | | 1978 | 50.401995051769 | | 1977 | 50.468699485142 | | 1976 | 50.553022389974 | | 1975 | 50.616157550686 | | 1974 | 50.566901428529 | | 1973 | 50.438669933951 | | 1972 | 50.299817476592 | | 1971 | 50.146778857994 | | 1970 | 50.022954095069 | | 1969 | 50.00280723532 | | 1968 | 50.047726861405 | | 1967 | 50.090451597036 | | 1966 | 50.134994329731 | | 1965 | 50.181966227775 | | 1964 | 50.231970037431 | | 1963 | 50.286855202331 | | 1962 | 50.344562288339 | | 1961 | 50.403288264212 | | 1960 | 50.455348360303 |
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