| Year | Value | | 2022 | 50.539725865438 | | 2021 | 50.56014465753 | | 2020 | 50.581865395691 | | 2019 | 50.599414205631 | | 2018 | 50.613582030758 | | 2017 | 50.627073173781 | | 2016 | 50.637440529315 | | 2015 | 50.643852841893 | | 2014 | 50.64755419605 | | 2013 | 50.649392073291 | | 2012 | 50.649355033282 | | 2011 | 50.64799641082 | | 2010 | 50.64815137427 | | 2009 | 50.649509893529 | | 2008 | 50.648876948343 | | 2007 | 50.646888713067 | | 2006 | 50.644401067031 | | 2005 | 50.641845281118 | | 2004 | 50.63979202299 | | 2003 | 50.638284176639 | | 2002 | 50.636679355539 | | 2001 | 50.634369400621 | | 2000 | 50.62848587839 | | 1999 | 50.620556434807 | | 1998 | 50.615725606839 | | 1997 | 50.61075036958 | | 1996 | 50.603597973084 | | 1995 | 50.595663560393 | | 1994 | 50.587135535826 | | 1993 | 50.578476892909 | | 1992 | 50.568636912064 | | 1991 | 50.556804455624 | | 1990 | 50.544120078264 | | 1989 | 50.531060659273 | | 1988 | 50.519858943621 | | 1987 | 50.510453302286 | | 1986 | 50.502492396587 | | 1985 | 50.497443296926 | | 1984 | 50.495292479674 | | 1983 | 50.495563464405 | | 1982 | 50.496168472454 | | 1981 | 50.496879713697 | | 1980 | 50.499612748865 | | 1979 | 50.506873731441 | | 1978 | 50.515427461184 | | 1977 | 50.521730323206 | | 1976 | 50.528105267659 | | 1975 | 50.535369544817 | | 1974 | 50.53822337586 | | 1973 | 50.534248791067 | | 1972 | 50.52851608214 | | 1971 | 50.521858157352 | | 1970 | 50.517074469858 | | 1969 | 50.515343422722 | | 1968 | 50.516608906594 | | 1967 | 50.520290907457 | | 1966 | 50.526882055525 | | 1965 | 50.538103194281 | | 1964 | 50.550557349318 | | 1963 | 50.558946440404 | | 1962 | 50.5684513283 | | 1961 | 50.587486392856 | | 1960 | 50.616869195029 |
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