| Year | Value | | 2022 | 50.493387016105 | | 2021 | 50.49373652455 | | 2020 | 50.49075149427 | | 2019 | 50.49030606863 | | 2018 | 50.494976808453 | | 2017 | 50.503375174125 | | 2016 | 50.51360094857 | | 2015 | 50.522949256959 | | 2014 | 50.534881634513 | | 2013 | 50.54740970904 | | 2012 | 50.556787442138 | | 2011 | 50.56959244946 | | 2010 | 50.587763447813 | | 2009 | 50.606653597264 | | 2008 | 50.622821022785 | | 2007 | 50.633651310681 | | 2006 | 50.644229449811 | | 2005 | 50.6554932582 | | 2004 | 50.665647826221 | | 2003 | 50.677618707104 | | 2002 | 50.683206569096 | | 2001 | 50.683348802269 | | 2000 | 50.68690499961 | | 1999 | 50.693019084834 | | 1998 | 50.699531189562 | | 1997 | 50.703927585825 | | 1996 | 50.7107305297 | | 1995 | 50.722389416161 | | 1994 | 50.738737701188 | | 1993 | 50.75196225142 | | 1992 | 50.759450475352 | | 1991 | 50.769390211608 | | 1990 | 50.78226356751 | | 1989 | 50.795367348006 | | 1988 | 50.806363564533 | | 1987 | 50.815276802909 | | 1986 | 50.820808911679 | | 1985 | 50.822954001029 | | 1984 | 50.816689766429 | | 1983 | 50.803064982132 | | 1982 | 50.785305359149 | | 1981 | 50.763827484429 | | 1980 | 50.743443227772 | | 1979 | 50.724028530314 | | 1978 | 50.703398839193 | | 1977 | 50.677968449242 | | 1976 | 50.646724373976 | | 1975 | 50.612945235809 | | 1974 | 50.568810999116 | | 1973 | 50.51491995312 | | 1972 | 50.459435852752 | | 1971 | 50.400354962865 | | 1970 | 50.350812360443 | | 1969 | 50.309487531286 | | 1968 | 50.265247163595 | | 1967 | 50.223592603142 | | 1966 | 50.184996587082 | | 1965 | 50.145783051621 | | 1964 | 50.103413471422 | | 1963 | 50.059995739565 | | 1962 | 50.016743291587 | | 1961 | 49.974577688625 | | 1960 | 49.918377351577 |
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