| Year | Value | | 2022 | 49.806218531917 | | 2021 | 49.804071540082 | | 2020 | 49.80363420166 | | 2019 | 49.805362058567 | | 2018 | 49.80906434866 | | 2017 | 49.815768171093 | | 2016 | 49.826593437695 | | 2015 | 49.837450108817 | | 2014 | 49.846588255084 | | 2013 | 49.858233095751 | | 2012 | 49.872629402365 | | 2011 | 49.889719940281 | | 2010 | 49.909283332018 | | 2009 | 49.931924905499 | | 2008 | 49.955472118086 | | 2007 | 49.979384916026 | | 2006 | 50.004949055599 | | 2005 | 50.034662627091 | | 2004 | 50.067535215831 | | 2003 | 50.103323421447 | | 2002 | 50.142362239006 | | 2001 | 50.181055801257 | | 2000 | 50.217668020279 | | 1999 | 50.255522220367 | | 1998 | 50.296603436322 | | 1997 | 50.33876562669 | | 1996 | 50.382658145344 | | 1995 | 50.433439166097 | | 1994 | 50.487047015637 | | 1993 | 50.529614098643 | | 1992 | 50.567990168376 | | 1991 | 50.612617974099 | | 1990 | 50.628969727319 | | 1989 | 50.63247945242 | | 1988 | 50.660619167695 | | 1987 | 50.648065631714 | | 1986 | 50.62481438642 | | 1985 | 50.63537852359 | | 1984 | 50.627571355757 | | 1983 | 50.612336708325 | | 1982 | 50.624725817184 | | 1981 | 50.640804222964 | | 1980 | 50.627190505033 | | 1979 | 50.616406030331 | | 1978 | 50.618445111243 | | 1977 | 50.617746489307 | | 1976 | 50.615570167168 | | 1975 | 50.621628702459 | | 1974 | 50.635973622686 | | 1973 | 50.648635732276 | | 1972 | 50.651775612325 | | 1971 | 50.646834470976 | | 1970 | 50.640972854294 | | 1969 | 50.633770143794 | | 1968 | 50.626805830831 | | 1967 | 50.617130952051 | | 1966 | 50.603766656545 | | 1965 | 50.599459647074 | | 1964 | 50.605284566381 | | 1963 | 50.611656993623 | | 1962 | 50.619806228365 | | 1961 | 50.627255553321 | | 1960 | 50.631131367774 |
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