| Year | Value | | 2022 | 50.345772366645 | | 2021 | 50.356482602608 | | 2020 | 50.367323054755 | | 2019 | 50.373541156423 | | 2018 | 50.375658201793 | | 2017 | 50.376550972705 | | 2016 | 50.376061606098 | | 2015 | 50.374902394698 | | 2014 | 50.37316879049 | | 2013 | 50.372895697095 | | 2012 | 50.37092698566 | | 2011 | 50.364826631091 | | 2010 | 50.35840923544 | | 2009 | 50.354448043705 | | 2008 | 50.350215015102 | | 2007 | 50.343721953965 | | 2006 | 50.339355147372 | | 2005 | 50.334300176398 | | 2004 | 50.324329935751 | | 2003 | 50.316245794039 | | 2002 | 50.309292740363 | | 2001 | 50.301533854553 | | 2000 | 50.293700373483 | | 1999 | 50.285840204958 | | 1998 | 50.277199804099 | | 1997 | 50.266338663993 | | 1996 | 50.255157087448 | | 1995 | 50.242731708274 | | 1994 | 50.229473588661 | | 1993 | 50.21691060018 | | 1992 | 50.203229857425 | | 1991 | 50.186021102536 | | 1990 | 50.169547218725 | | 1989 | 50.154259443522 | | 1988 | 50.137978876499 | | 1987 | 50.119449216829 | | 1986 | 50.100910648011 | | 1985 | 50.082543338993 | | 1984 | 50.062267466465 | | 1983 | 50.043332221954 | | 1982 | 50.025046921426 | | 1981 | 50.006480148571 | | 1980 | 49.990784675656 | | 1979 | 49.977492013837 | | 1978 | 49.965996692242 | | 1977 | 49.95716571859 | | 1976 | 49.949675153011 | | 1975 | 49.941767679422 | | 1974 | 49.933280808761 | | 1973 | 49.925086435983 | | 1972 | 49.91723039572 | | 1971 | 49.91006330656 | | 1970 | 49.902966624702 | | 1969 | 49.894717972513 | | 1968 | 49.885912628829 | | 1967 | 49.876486377863 | | 1966 | 49.870977139535 | | 1965 | 49.909197374543 | | 1964 | 49.943245537999 | | 1963 | 49.928972795808 | | 1962 | 49.910899282985 | | 1961 | 49.893455998263 | | 1960 | 49.878488346629 |
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