| Year | Value | | 2021 | 5.2984505969012 | | 2020 | 5.2933705867412 | | 2019 | 5.2933705867412 | | 2018 | 5.2933705867412 | | 2017 | 5.2933705867412 | | 2016 | 5.2933705867412 | | 2015 | 5.2933705867412 | | 2014 | 5.2933705867412 | | 2013 | 5.2933705867412 | | 2012 | 5.2933705867412 | | 2011 | 5.2933705867412 | | 2010 | 5.2933705867412 | | 2009 | 5.2933705867412 | | 2008 | 5.2933705867412 | | 2007 | 5.2933705867412 | | 2006 | 5.2933705867412 | | 2005 | 5.2933705867412 | | 2004 | 5.2838877317755 | | 2003 | 5.2744053848108 | | 2002 | 5.2649225298451 | | 2001 | 5.2554396748793 | | 2000 | 5.2357973075946 | | 1999 | 5.2212344424689 | | 1998 | 5.2117515875032 | | 1997 | 5.2022692405385 | | 1996 | 5.1927863855728 | | 1995 | 5.178223520447 | | 1994 | 5.1585811531623 | | 1993 | 5.1490982981966 | | 1992 | 5.1396154432309 | | 1991 | 5.1301330962662 | | 1990 | 5.1206502413005 | | 1989 | 5.1111673863348 | | 1988 | 5.09152501905 | | 1987 | 5.0820421640843 | | 1986 | 5.0725593091186 | | 1985 | 5.0529169418339 | | 1984 | 5.0434340868682 | | 1983 | 5.0187112014224 | | 1982 | 5.2664043688087 | | 1981 | 5.5140970281941 | | 1980 | 5.7617896875794 | | 1979 | 6.0094828549657 | | 1978 | 6.257175514351 | | 1977 | 6.5048681737363 | | 1976 | 6.7525613411227 | | 1975 | 7.000254000508 | | 1974 | 6.9950688831275 | | 1973 | 6.9950688831275 | | 1972 | 6.9849016318438 | | 1971 | 6.9696507549184 | | 1970 | 6.9696507549184 | | 1969 | 6.9442326267094 | | 1968 | 6.9442326267094 | | 1967 | 6.9340653754258 | | 1966 | 6.9340653754258 | | 1965 | 6.9086472472167 | | 1964 | 6.9086472472167 | | 1963 | 6.9086472472167 | | 1962 | 6.9086472472167 | | 1961 | 6.9086472472167 |
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