| Year | Value | | 2022 | 51.09823817813 | | 2021 | 51.13062019593 | | 2020 | 51.163179462116 | | 2019 | 51.195018171553 | | 2018 | 51.227461259854 | | 2017 | 51.261297369642 | | 2016 | 51.296220839297 | | 2015 | 51.330894855304 | | 2014 | 51.364200608767 | | 2013 | 51.397415619752 | | 2012 | 51.432518418951 | | 2011 | 51.470153319271 | | 2010 | 51.509334076567 | | 2009 | 51.495789589925 | | 2008 | 51.426282454468 | | 2007 | 51.352882137132 | | 2006 | 51.276084461018 | | 2005 | 51.195932530192 | | 2004 | 51.109488649442 | | 2003 | 51.016291374116 | | 2002 | 50.915824805648 | | 2001 | 50.80707810469 | | 2000 | 50.692015523978 | | 1999 | 50.634403364887 | | 1998 | 50.638842446006 | | 1997 | 50.642457792956 | | 1996 | 50.645039252888 | | 1995 | 50.64679805539 | | 1994 | 50.648401785458 | | 1993 | 50.650047241279 | | 1992 | 50.652803509398 | | 1991 | 50.656096773664 | | 1990 | 50.659585795648 | | 1989 | 50.665273493883 | | 1988 | 50.672947558963 | | 1987 | 50.681605425974 | | 1986 | 50.690679322362 | | 1985 | 50.699070401476 | | 1984 | 50.707182278309 | | 1983 | 50.715916798189 | | 1982 | 50.724813517736 | | 1981 | 50.734478304327 | | 1980 | 50.745563593382 | | 1979 | 50.757424595598 | | 1978 | 50.770183608086 | | 1977 | 50.784414405065 | | 1976 | 50.795834218088 | | 1975 | 50.804380498551 | | 1974 | 50.813665447249 | | 1973 | 50.823147118994 | | 1972 | 50.833388957711 | | 1971 | 50.844207711932 | | 1970 | 50.855595318996 | | 1969 | 50.868125057396 | | 1968 | 50.88170536959 | | 1967 | 50.89580702991 | | 1966 | 50.910693943625 | | 1965 | 50.92813608512 | | 1964 | 50.947388077649 | | 1963 | 50.967241108009 | | 1962 | 50.988861656434 | | 1961 | 51.013925413679 | | 1960 | 51.042855162423 |
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