| Year | Value | | 2021 | 4.7712547019653 | | 2020 | 4.803663056467 | | 2019 | 4.7001340363907 | | 2018 | 4.7639729191723 | | 2017 | 4.7628194445101 | | 2016 | 4.67389174781 | | 2015 | 4.6256066839954 | | 2014 | 4.6128247128595 | | 2013 | 4.6255146230333 | | 2012 | 4.6415339662231 | | 2011 | 4.6265760496566 | | 2010 | 4.6280137944528 | | 2009 | 4.6281869088933 | | 2008 | 4.6642312598431 | | 2007 | 4.8734400395505 | | 2006 | 4.8515009446711 | | 2005 | 4.8248715623544 | | 2004 | 4.8559715340912 | | 2003 | 4.9078365714805 | | 2002 | 4.8545599020154 | | 2001 | 4.8322653512972 | | 2000 | 4.7803338692796 | | 1999 | 4.943823609843 | | 1998 | 5.0075241064469 | | 1997 | 4.9963659458858 | | 1996 | 5.0784937534796 | | 1995 | 5.0957294466095 | | 1994 | 5.1022816701926 | | 1993 | 5.1583725643024 | | 1992 | 5.0677635007237 | | 1991 | 4.9736554479999 | | 1990 | 4.7823000241399 | | 1989 | 4.7558975720255 | | 1988 | 4.7631306324563 | | 1987 | 4.7422865913134 | | 1986 | 4.6821417341351 | | 1985 | 4.6369796449921 | | 1984 | 4.5945397519915 | | 1983 | 4.5343574824318 | | 1982 | 4.5333420035043 | | 1981 | 4.4708330401212 | | 1980 | 4.3958657536858 | | 1979 | 4.604395242214 | | 1978 | 4.5256510867851 | | 1977 | 4.5771376499502 | | 1976 | 4.6284460589174 | | 1975 | 4.6367302291152 | | 1974 | 4.6866134045 | | 1973 | 4.7005094319286 | | 1972 | 4.6374263223671 | | 1971 | 4.5397981698285 | | 1970 | 4.4806511869036 | | 1969 | 4.4619450627858 | | 1968 | 4.4493852365924 | | 1967 | 4.463726598416 | | 1966 | 4.4456440117688 | | 1965 | 4.4631030609454 | | 1964 | 4.4311244963822 | | 1963 | 4.4053813065248 | | 1962 | 4.3926433267684 | | 1961 | 4.400036699634 |
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